You didn't write that the ominous figure sounded vaguely like Fumito in the actual story, only in your author's note, you need to fix that. That's no way to tell a story.
It's bad form to change tenses and it interrupts the flow of the story, so never do that. Finally about the letter, Tadayoshi speaks much more formally than that: For instance, instead of:

"Take care of her for me until I have found a permanent place to stay. Reparations will probably take really long, so please be patient. There is no return address because I have no address."

He would write:
Please take care of her for me until I have found a permanent place of residence. Reparations will probably take time, so I would ask that you be patient. I apologize for the lack of a return address, but I am afraid I have none at this time."

I recognize that you're new at this, and I apologize for the harsh tone of the review, but I very much encourage you to keep writing, and to take any advice you get. Practicing is always good. So is reading, though published work from the literature section is typically better for improving your skills than fanfiction.

So far it's decent. So I take it that you're writing this with the plan for it to be more mystery and less betrayal? That sounds like a plan. I'd like the opportunity to see Nene and Nono as being like Hikaru and Kauru again. It was kind of terrible to see Saya betrayed by literally everyone she knew. Especially when her two best friends had been a pair of scamming, thieving, lying murderers. And the fact that they had managed to get all they had on their records at only fourteen is just disturbing.

You already have some slight romance here with the lip thing! Fumito unknowingly caused the blood to go bad. Ew, is he really testing with mold? I agree with Saya. This is the weirdest class experiment ever. Even my life & physical science classes don't use food (except strawberries for DNA extraction). Other than the blood, Fumito might also want to watch out for Kagusa. Update soon!

Cool three chapters

You're back! I was wondering what the pipes were about, since the twins were obsessed with that problem. Still, the Blood-C characters having a picnic is weirdly OOC. I can't imagine the peace that's floating around! x_x What a suspicious basket. Did Fumito purposely leave the basket behind for Kagusa to pick up? The accident scene was descriptive, but I don't know much about cliffs & beaches. :/ Saya's blood stopped the water...just like part of the fire. Fumito is discovering something for his future maniacal plan. Update soon!

OMG! 3 days late! Happy Belated 16th Birthday! I can't believe even Fumito doesn't know his way around. I like ramune, especiallly the fruint-flavored versions. I assume "Kagusa" means "sweet grass," & "Hisuidou" means "jade wisteria." So much green compared to the usul red. What a suspicious letter. Yeah, imagine fireballs in the sky. Give Saya a reason not to leave after seeing a creepy person. Update soon!

AWESOME! ILL START WRITING TOO! I JUST BARELY FINISHED WATCHING THE FIRST 12 EPISODES!

Wait, there's a category for Blood-C? OMG, I'm so behind! I love Blood-C, in addition to Junketsu Paradox. I absolutely hate fires. They consume almost everything in your way. So Saya's blood actually "extringuished" the trail of fire that caught her? I want to ask how that fire can hold on to her in the first place. "Ukishima" means "floating island," & "Kiyomizu" means "clear water." I totally agree on Saya when it comes to searching for a location on foot. It's tiring & confusing. Did Fumito just wreck Saya's map? He'd BETTER help her get to the shrine. Update soon!