Note: This ficlet was written in response to a prompt on Tumblr. As timeline goes, it predates the actions Mille takes in Darkness, postdates A Kind of Poison and Nature of the Game.
"These things happen" has become a mantra they say in response to weaknesses in the time stream that allows them to walk at will through the worlds that others cannot access. Most times, though, these things happen by accident and they have to find their way back. Ryo was the past, Monodramon the stabilizing present, Millenniumon the future. With Monodramon, there was little danger of their powers accidentally activating. Without, well…
"This looks familiar," Ryo mutters as they walk through a younger Digital World. At his age and after far too many accidents that Millenniumon was sure were intentional, the going is harder and he has to watch for any rocks in the path that might turn his ankle. Millenniumon, in the body of a younger man, drifts behind out of a consideration that Ryo would never acknowledge. Their relationship had always been particularly delicate, and a certain balance must be maintained.
A moment later and Millenniumon comes to the same conclusion. Ryo shoots him a warning look, and Millenniumon responds with far too much innocence. Not that Ryo would buy it, of course. This early on, there was too little to change even if he wanted to modify their past.
After a while, Ryo obeys the complaints of the body and settles under a tree to rest. Millenniumon waits until his breathing shallows to place a light, affectionate kiss on his partner's brow just before relocating himself. It's a trick of programming that allows him to do so within the confines of the Digital World, and he's fairly sure he's the only digimon to ever figure it out. This, naturally, only confirms that he is a god.
First, he pays a visit to his younger self, a beast with entirely too much power and not enough wisdom to use it well. A result of his impatience to become stronger and the lack of a partner to show him that there was more in life than power. He steps up to the hideousness of his past, tells him in no uncertain terms that he's an idiot, and folds space around himself and flees before the cannons light up.
Miles away, a young boy and an agumon nap under a similar tree. Millenniumon cares not for the digimon and never did, but the boy's youth sends a twinge of regret into his digicore and he tamps it down before it gets too distracting. It always should have been him at his partner's side, not these pretenders. This is not about them, he reminds himself as he removes his coat and kneels at the boy's side.
The boy wakes up just as he tucks the coat around him. Blinking, the boy sits up and gives him a curious look that was unmarred by the distrust that colored Ryo's later experiences. Vaguely Millenniumon wonders if it's sentiment and regret that will end up cracking open his digicore and destroying him, rather than some heroes in a final dungeon in some distant future.
"Who're you?" the boy asks as he straightens his sweater self-consciously.
"A possibility," he responds with a slight smile that he hopes is reassuring. All the boy would see is a middle-aged man with dark hair and copper-rimmed glasses, not the two-headed monstrosity with which he will become familiar. "For what it's worth, I'm sorry."
He doesn't give the boy time to ask, and disappears again before the agumon wakes up.
Ryo doesn't wake up until an hour later, at which point Millenniumon has already found a weakness in time through which they can return. His partner doesn't comment on the missing coat, but he can tell that Ryo knows he tampered with the past. They say nothing as they weave their shared power into the weakness between times so that they can go where they want, and it takes only the time between one breath and another before they return home.