asking me this question was mistake #1.. alas the deed is done prepare for Information. seriously though thank you for asking goon nation that is very very kind of you. !!!!!!!! :3
hcs that make sense (have some sort of tie to canon?):
he is afraid of snakes and has never outgrown this fear (stems from his Past with orochimaru)
when he started anbu his taijutsu was absolute ass because he was mainly trained to use his mokuton ninjutsu so kakashi helped him practice
he cannot use genjutsu but he also isn't very susceptible to it... (has to do with emotional component of genjutsu.. training from a young age to suppress his emotions allowed him to be more resistant to the mind games if u will)
had a very hard time adjusting to Anbu Life after kakashi left and would often go looking for him/observe him from a distance. Lowkey not even making this up as it occurred in the show but
now for the reason he was able to adapt to hashirama cells (unlike everyone else). now this whole "putting hashirama cells into people" is a whole load of hooey like is it s skin graft? are they eating the cells? how are they getting there. so i think it could make sense that they get their via organ transplant possibly. specifically a bone marrow transplant... now what orochimaru did not account for is that a healthy person's immune system would go flipping crazy if foreign cells were suddenly introduced into the body and thus rejection/failure would occur. here's where it gets Crazy. in my hc tenzo was born with/acquired some form of aplastic anemia. idk maybe he has fanconi anemia or took some chloramphenicol I don't know. anyway as an infant he had no immune system basically. and as it turns out the treatment for these diseases is a bone marrow transplant. So by complete accident orochimaru cured his aplastic anemia with hashirama cells (who happened to be a perfect donor match. Thanks girl!)
hcs that are completely pulled out of my ass:
he was not originally born in the leaf but some rando village nearby (like The Grass Village)
he does not resemble either of his parents
he eats the same meals every day because it's easier not to think about it
he does not eat meat and occasionally eats fish
he likes dark/somewhat cramped spaces like a freak.. if he is overwhelmed or smth he will happily build a little dome to sit in
he always wanted to learn medical ninjutsu (which he knew he could do very well as he has hashirama's cells). again he was never trained due to the emphasis on refining his mokuton in the anbu/foundation so he only gets the chance after the war and such and either asks sakura or tsunade for help . AGGGHHHHH
and, of course, he has an accessory spleen (just like 10-30% of the population)
ok that is enough thank you again. That was a whole heap of nonsense and there is certainly more rattling in the rusted cogs of my brain but..erm..Yeah. Ok thank you third time have a wonderful day and night. <3