I think one of the most heartbreaking headcanons I have is that back when he was growing up in the Shimura house, Tenko got the opportunity to watch one of UA’s sports festivals once when no one else was around or were otherwise occupied (Kotaro being on a business trip and everyone else running errands).

During the tournament portion, he saw how one particular student was able to take away his opponent’s quirks, then beat those opponents using nothing but physical training and good strategy. Watching that student win fight after fight while practically quirkless himself blew Tenko’s mind, because it showed how he could still have a chance at being a hero even if he didn’t have a quirk, he just had to specialize in other ways.

While that student didn’t win the festival, he did manage to make it to third place. And as Tenko watched the student receive his bronze medal, he whispered in awe to the television…

“You’re so cool Aizawa!”