HI. HELLO. sorry this took two months lmao BUT i have a few! my fiance loves ivan, he's one of his favorites, and while i don't have too many headcanons about him yet, there's a couple i can share!

note that these apply almost solely to my fic universes, mostly to BSPverse (next gen verse), aside from the first one. do not take this as like, how i think he is in canon lmao

• fyodor absolutely did not give him a lobotomy first and foremost idc what canon says, usually i'm okay with medical inaccuracies to a degree but not when it's procedures that aren't understood at all to start with by most of the general public, AND have been used as a tool for oppression, just to explain why i'm so hardline about this. anyway what he effectively did was brainwash ivan into believing he'd done it using a lot of cult brainwashing tactics and not like, an ability, as some have theorized (bc fyodor would need someone else to do that given his ability can't do that, and let's be honest, i don't think he'd do that for such a delicate situation requiring ivan to trust him and only him)
• he's nonbinary transmasc and gay
• in BSPverse, he and fyodor are one of only a handful of couples who are married before the series officially starts (atsushi acquisition, which in BSPverse, takes place in 1999). they got married because ivan wanted fyodor to "take all of him" aka wanted to fuck and fyodor was like "not before marriage hashtag christian life" so ivan was like "ok let's get married" and fyodor was like "sounds legit" not thinking that he would ever actually care about ivan beyond his plan (spoiler alert: he does! rip fyodor's attempt to remain isolated)
• ivan gets incredibly irritated if anyone enters the kitchen while he's using it so fyodor warns any guests he doesn't want immediately killed to just stay away from it lmao. unless he wants them dead, in which case ivan will squish them like little bugs with the precipice the moment a single molecule of their body crosses the threshold
• he was a child soldier in the great war. russia wasn't involved directly, but ivan was shipped off to and used by the UK, and then returned to russia after the war where he was then unceremoniously shoved into a mental hospital due to The Horrors Of War:tm: and his PTSD causing him to lash out with his ability, where fyodor later found him