Based on Mario Party: Island Tour, I thought of this one-shot. I hope you enjoy.
"It's time to finish this, Bowser!" Toad exclaims as everyone reaches the final floor to Bowser.
"You think that it's going to be so easy?" Bowser asks.
"We don't think it will: we know it will." Luigi says.
"Then you're going it have to fight me first!" Bowser stomps the ground and roars as Mario, Peach, Daisy, Wario, Waluigi, and a rogue Boo get ready for battle alongside Luigi and Toad.
"Here we go!" Mario charges in and jumps around him, trying to get behind him.
"I packed when we got here!" Peach tosses Luigi a fireflower, and Luigi starts to shoot fireballs at Bowser.
"Come here! I will crush you!" Bowser charges at Luigi, but Mario grabs his tail and spins him around.
"So long, a'Bowser!" Mario exclaims as he tosses him off the edge. Bowser grabs on, and barely makes it back up.
"No more games!" Bowser charges at Peach, but Wario grabs his horns and thrusts him away from Peach into a wall.
"I got this!" Luigi jumps on Bowser's head and shoots fireballs.
"No, I can't lose like this!" Bowser screams as he gets hit. He falls to the ground in pain, and Mario finishes him off, grabbing his tail again and tossing him off.
"Yes! We did it!" Waluigi cheers.
"You didn't even do anything!" Toad says.
"Neither did you!" Waluigi barks back.
"Hey! No time for that! It's time to shut down this Dark Bubble Machine once and for all!" Daisly breaks up the fight. With Mario and Luigi's double ground pound, they destroy the machine and the bubbles begin to disappear.
"Yes! That did it!" Peach says.
"Yahoo!" Mario cheers.
"Don't celebrate to hard, Mario." Bowser appears back up on the tower again with his Clown Car. "That wasn't the real machine. Look." Bowser pushes a button, and the bubbles continue to be made.
"What? No!" Wario face-palms.
"Who made so many of these? It must have been Bowser Jr, wasn't it?" Toad asks.
Bowser goes silent. He gets abnormally angry about the subject. "Don't bring him up, do you hear me?" Bowser goes from angry to upset.
"Huh? Is... there something we don't know about?" Luigi asks the others.
When he says that, Peach begins to act sheepish.
Bowser starts to whistle a tune, and a single tear goes down his eye. Snapping out of it, Bowser remembers about the heroes. "It's time to say goodbye." Bowser knocks them all off of the tower to the bottom.
"What was with Bowser back there?" Waluigi asks.
"I think I may know." Peach finally decides to speak up.
"What?" Toad asks.
"Well, if I show you, please don't freak out." Peach says.
Mario nods, as well as the others.
Peach leads them to her castle and to a door labeled 'Guest Room'.
"Do you have a visitor?" Luigi asks.
"Well, more like a temporary home." Peach opens the door, and everyone gasps. There lays the yellow and green koopa with his hair in an orange ponytail and his signature bib. He is just laying down on the bed, whistling the same tune Bowser was whistling.
"Bowser Jr?!" Everyone asks in shock.
"Surprised to see me?" Bowser Jr replies.
"Honey, did you even touch your lunch?" Peach asks.
"I'm not hungry." Bowser Jr lays back down on the guest bed, motionless.
"Oh, I let him stay here for now. It seemed like a bad idea, but he's so depressed he doesn't even want to capture me, and he hardly eats anything I give him." Peach explains. "Something must have happened between him and his father."
"Could you get him to talk?" Toad asks.
"No, he won't tell me. But he does tell me it was bad." Peach explains. "I think he would like some privacy, just him and I."
Everyone leaves the room, leaving open a talk just Bowser Jr and Peach.
"I know you don't want to say anything, but I'm here to help you. I can't help you if you won't tell me what's wrong." Peach discusses.
Bowser Jr thinks it over, and finally decides to talk, tears flowing down his eyes.
"Papa won't stop! He's gone out of control! I tried to help him, but he shunned me!" Bowser Jr yells.
"What is Bowser doing?" Peach asks.
Bowser Jr calms down, and begins to remember the horrible flashback.
"Papa, you're going to do what?" Bowser Jr asks.
"I'm taking your fancy mind-control bubble device you built, and I'm going to use it on everyone in the Mushroom Kingdom!" Bowser exclaims.
"But Papa, that machine is only used for workers who will not listen to your command! It's not meant to be used on anyone else but Goombas, Koopa Troopas, and other minions!" Bowser Jr explains.
"I don't care what consequences come with using it on other people, I want to take over! Even if it means controlling everyone to do my bidding!" Bowser snaps at his son. "This is what we've been trying all these years to accomplish!"
"No! You aren't remembering our directive!" Bowser Jr tries to explain, but Bowser cuts him off.
"Of course this is what our directive was! We do the things we do to take over everything!" Bowser screams.
"That's not it!" Bowser Jr corrects him.
"Then what is it?" Bowser asks.
"It's..." Bowser Jr wants to explain, but once again gets cut off.
"That's it! I've had enough of your talking! Am I going to have to ground you?" Bowser asks.
"It doesn't matter what you do to me, I can't let you soil what we were supposed to do as a team!" Bowser Jr says.
"Fine then, maybe we weren't meant to be a team after all..." Bowser says.
"What?" Bowser Jr asks in shock.
"Guards, take him away! I don't want to see my son's face around here! And he isn't welcome back into my tower until he thinks about who's side he's on!" Bowser sends his guards to kick Junior out of the tower, and onto the streets and the pouring rain.
"Papa... what happened to you?" Junior asks rhetorically.
"Junior? What are you doing out here?" Peach asks, holding an umbrella to block the rain.
"I don't want to talk about it, Mama Peach." Bowser Jr sits on the curb.
Peach thinks for a moment, standing in the rain. "Would you... like to stay with me for the night?"
"Huh? You would really do that?" Junior asks.
"Nobody ever deserves to sleep out here in the rain." Peach says.
"Th-Thank you, Mama Peach." Bowser Jr slides under Peach's umbrella, to keep him dry.
Junior finishes his story, trying not to cry.
"So that's why he left you out in the rain. I think the right thing to do is to go talk to him, and settle your differences." Peach says.
"But... how? It's not like he can just let me in again." Bowser Jr explains.
"By showing him you are worth it to him." Peach says.
"But how can I..." Junior then gets an idea. "I know what I must do."
Junior dashes out of the room, knocking everyone else over, since they were eavesdropping on Peach and Junior's conversation. Junior stops for a moment.
"Where is the Garage?" Junior asks.
"Down the stairs, to the left. Why?" Toad asks.
"Because I'm going to need metal. Lots and lots of metal." Junior dashes away.
"What is he doing?" Luigi asks.
"He's going to raid his own father's castle!" Wario realizes.
"But how will that show his father that he is worthy?" Daisy asks.
"Because he will defeat his own father, and prove that his is eviler then Bowser himself!" Waluigi answers.
Junior starts to get to work, and in no time, a machine is ready.
"Should I have done that?" Bowser reconsiders.
"That kid was for the wrong side, sir. You did the right thing. He needs a few days to think it over." Kamek answers.
"Sir! Incoming giant robot!" A goomba replies. Bowser looks outside to see the Gigantic Bowser Robot Junior made in Mario Sunshine.
"Now, let's take that tower by storm!" Toad exclaims.
"What? We have a visitor? It looks like Bowser Jr! Here to try to stop me from making more bubbles, no doubt. Oh, but it's far too late. Nothing can stop me now, not even you, Son!" Bowser laughs. "Take down the Robot!"
"Alright, big fella! Let's crash this party!" Bowser Jr jumps into the cockpit and starts to walk it towards the castle.
"Man the catapults!" A Hammer Bro commands. Goombas and Koopa Troopas do as he says. "Ready... fire!"
"Brace yourself!" Luigi hollers from below.
"Activating shields!" Bowser Jr tries to get the shields online, but the fireball hits him before it's ready. The chest plate falls off, and a gem smashes at the bottom. "That powered up my shields! You have no idea how much work I put into that!" Bowser Jr roars.
Bowser Jr operates the legs and kicks the fireball back at the minions operating the catapult, destroying it. The pieces of the catapult collapses on the Goomba Tower, destroying them as well.
"Alright!" Daisy cheers.
"Aww, you knocked over my Goomba Tower, boo hoo... I have a million of those!" Bowser says from above. "It's called Tough Love, and it makes you tough! How do you think I got so tough?"
"Go, Junior, go!" Wario hollers.
Junior grabs the drawbridge, which is raised, and is pulling it down with the Robot's arms.
"We need lava!" The Hammer Bro orders.
"And a Chain Chomp!" The other Hammer Bro koopa troopas do as they say again and get the lava ready.
"That's right, buddy! Heave, hoe!" Junior chants.
"Watch out!" Mario warns. The minions send the Chain Chomp in first, followed by the lava. Bowser Jr grabs the chainchomp, and the lava only hits the Chainchomp, leaving Junior's robot undamaged and the Chain Chomp destroyed.
"More lava! No Chain Chomp this time!" The First Hammer Bro smacks his brother on the back of the head.
"Grr! I should have spent more time training my Chain Chomps! I would have special place in my black heart for you son, but it's gone now. You will lose, and see if I care?" Bowser replies.
With another try, Junior grabs the drawbridge and continues to try to pry it out. The second serving of lava comes, this time with no way to protect it. Knowing what's going to happen, Junior gets out and stands on the arm of the robot, ready. The lava hits the robot, and shortens it out. The lava is so hot, it's arms melt off, leaving the robot arms stuck in the drawbridge. Junior jumps into the castle while the robot falls into the robot moat.
Junior sees Mr. Blizzard waiting for him, and he kicks him in the chest, sending him backwards. Junior then trips Mr. Blizzard, making him crash to the ground into a pile of snow.
"Really? You defeated Mr. Blizzard? That's... actually kind of impressive. I mean... HA! That means nothing." Bowser tries hard not to be impressed.
With Mr. Blizzard defeated, Bowser Jr lowers the drawbridge.
"Come on!" Bowser Jr signals everyone else to follow him.
"Nice work, Junior!" Luigi gives a thumbs up.
"Lets'i go!" Mario and the others follow him.
Bowser Jr runs up the tower, floor by floor. He soon reaches King Bomb-Omb, who tries to stop him by throwing Bomb-Ombs at him. Knowing that Bowser Jr has a lot of experience with Bomb-Ombs, he kicks them back at King Bomb-Omb, destroying him. Without stopping, Junior continues up.
"Ugh, poor King Bomb-Omb. Up in smoke. What's next, Bowser Jr. WHO ARE YOU?!" Bowser screams. "You're... you're almost as strong as me! Meh, whatever!"
With Bowser Jr almost to the top, there he sees his strongest opponent.
"Bring it on, Grandson!" Dry Bowser screeches. Bowser Jr tries to attack him, but he counters very easily and smacks down Junior. With a powerful punch, Junior goes down.
"Junior, please get up. For your father!" Peach exclaims. With that motivation, Junior gets back up and has an idea. He pulls out his Paintbrush and spreads it on the floor, making him slip and fall over. Junior then jumps over him, Dry Bowser unable to get up. Junior turns around as he runs off and throws a leftover bomb-omb at Dry Bowser, blowing him up.
"I can't believe it. Dry Bowser failed me? ARGH! Well, son, you leave me no choice... I'll have to face you myself! That will knock some sense into you!" Bowser warns. "Get ready!"
Junior makes it to the top the the tower, his father behind the doors.
"This is family business from here on. I have no choice but to go in alone." Bowser Jr stops the heroes at the doors. Junior kicks down the doors, with Bowser waiting for him.
"Good luck!" Toad hollers to him as he opens the doors, walks in, and shuts behind him.
"Look who decided to betray me!" Bowser yells.
"I didn't mean to betray you! I just wanted to talk to you, but you wouldn't let me in!" Bowser Jr yells back.
"It's far too late to talk now. All these years I've been going easy on you, because you were my son." Bowser replies.
"Were?" Junior asks.
"Yes. I have no son anymore." Bowser says.
Bowser Jr unleashes all of his anger on his father after he said that, clawing at his face.
"It's on!" Bowser roars.
Bowser and Bowser Jr go at it, no weapons or gimmicks. One-On-One hand-to-hand combat. Bowser Jr jumps over Bowser with such aerodynamic moves that Bowser can't grab him.
"You have no son? Well I have no father!" Junior dropkicks Bowser in the back, making him fall over.
"I don't even know you!" Bowser shoots fire, hitting Junior.
"I never knew you!" Bowser Jr tries to shoot back, only make a little ember.
"You can't even make a good fire. What kind of Koopa are you?" Bowser smacks Junior with the back of his hand. Junior is able to recover from his attack and return back, jumping on his head and hitting him repeatedly in the back of the head. Bowser grabs him and throws him off of his head, followed by a blast of fire.
"If you would only listen to me!" Junior explains. Bowser isn't listening. Bowser continues to hit Bowser Jr, knocking him down. Bowser laughs, but he hears him crying.
"Son?" Bowser asks as he walks over to him. Junior tricks him and slides under his legs to his tail.
"Don't you dare!" Bowser warns.
"You won't listen to me, so why should I listen to you?!" Junior screams as he spins him around and around by his tail, getting faster. He finally throws him off of the Tower, falling to his doom. "So long, a'Father." Junior replies as he goes to turn off of the machine. Suddenly, the entire castle starts to shake. Bowser Jr turns around in fear to see the 20-foot tall Koopa that is the horrifying transformation of Bowser.
"Papa?" Junior asks.
"That's not your father anymore, Junior! That can only be..." Luigi explains.
"Giga Bowser!" Mario finishes Luigi's sentence.
Without even trying, the feral beast slashes and smashes Junior around helplessly.
"There's no way Junior can beat his father now!" Peach exclaims.
Junior lays motionlessly on the ground. Suddenly, red aura starts to flow around his downed body. Junior's bib gets shredded up, his spikes on his shell become sharper and bigger, and his ponytail becomes bigger than his head. Junior's teeth become massive and his claws become extremely sharp. When the transformation is complete, a big red aura explosion occurs around him.
"Is that... Giga Bowser Jr?!" Wario gasps in horror.
The Giga forms charge at each other, causing massive havoc.
"We have to get out of here! We don't want to get caught in the crossfire!" Daisy warns. Everyone evacuates the Tower, except the two titanic beasts.
Just like the battle before, Giga Junior is too fast for Giga Bowser. With telepathic powers, Giga Junior can fly around him and teleport, leaving Giga Bowser in the disadvantage. However, Giga Bowser doesn't flinch from his attacks.
Giga Bowser roars and claws Giga Junior, sending him flying.
"Terra Koopa Fire!" Giga Bowser roars as it charges it's blast.
"Exa Koopa Ice!" Giga Junior screeches. Both blasts collide, and the battle is on to force their blast on the other. With Giga Bowser's amazing strength, he is obviously winning. Giga Junior tries his best to fight back, but then he gets an idea. Giga Junior starts to power down his blast, letting the blast get closer to him. He then puts up a shield, absorbing the blast. This powers him up, ready for a comeback blast.
"Hyper Fire-Ice Koopa Blast!" Giga Junior hits Giga Bowser with this blast double the power of his own. Giga Bowser collapses on the tower, and he remembers a biography entry of Bowser Jr made by Toad:
"He's maybe even more selfish than his dad, but he's also got a lonely side. What could all of this add up to one day? The world waits... and fears!"
Bowser then realizes what he has done as he returns back to Bowser, along with Junior. With both of them out of breath, and with Bowser down, Junior has him right where he wants him.
"We did so much together. Why did you turn to the good side?" Bowser asks.
"You idiot! Now that you're too tired to speak, I need to say something, so listen up!" Junior says.
"I didn't want any of this. The only reason I wanted to stop you is because of what we were supposed to do. Our plans are to bring our family together, not tear it apart! We started this to try to fill that void in our hearts. You know what I'm talking about. Real Mama... I never got to ever see her, but you used to talk about her all the time. How she loved you so much, and how I was made... naturally. That's why you loved me the most, Papa. I remember me asking you why you like to do the most things with me, and you said..." Junior explains.
"...Because that was when me and your real mother had love." Bowser says.
"Right. You were so caught up in this, Bubble Machine plan, you didn't think about me or why I am here today. You didn't even want to capture the princess anymore. You just wanted to take over everything, which feels like such an empty world to live in. Once you take over everything, what is there to do left? Nothing. Just sit around and enjoy what you've done. There is only so long before you feel lonely. And these people that you possess, they don't give you love out of their heart. They only love you because you tell them to." Junior finishes, and there is a moment of silence.
"Son... I..." Bowser says, but he doesn't know what to say.
"You don't need to say anything. I just... wanted to help you become a better Papa than you are. I noticed that you had trouble with your plans, and I only wanted to help. I know what you want me to do. You don't know me anymore, so I'll leave. Little did I know that I was so weak." Junior gets up to walk away, but instead, Bowser wraps him the warmest hug he's gotten. Junior can't help but cry.
"No, son. I'm the weak one. You were right about everything. I may be a tough Koopa on the outside, like my father, but I can't handle the pain of loosing Clawdia. She was the best Koopa in the world, and I would do anything to see that face one last time. I messed up big time, Son. I should have listened to what you had to say. I wouldn't have lost my way if it wasn't for this stupid machine!" Bowser lets go of Junior and smashes the real Bubble Machine himself.
"Papa, you..." Junior gasps speechless.
"That machine isn't worth anything compared to you, son." Bowser hugs him again. "Even though it might have seemed that I was upset when you stormed my own castle, inside, I was extremely proud of you, Junior."
"Really?" Junior asks.
"If you could enter an enemy castle like that, there's no way anything can stop us." Bowser replies.
"I love you, Dad!" Junior cries.
"I love you too, son!" Bowser cries as well.
"Do you think they're working it out up there?" Luigi asks.
Bowser and his son walk down the tower steps to the bottom.
"Hey! What are you doing on our property! Get out of here!" Bowser screams.
"And don't think you can hide Mama Peach from us forever!" Junior adds.
"Don't make us hurt you!" They both threaten.
Everyone runs off to the Mushroom Kingdom with Peach and the others.
"I think so, Luigi!" Daisy answers.