*claps hands lightly* whooo! You actually bothered to look up the info on Tania!
History fleshed out nicely. We know his father had fishing as his hobby - this can provide you with an anecdote about a fishing trip sometime or something to that effect : heck, maybe he either picked up a fondness for specific Yamatai fish... or ate so much he ended up disliking seafood ^_^
The mother bit makes a bit more sense now. His mother, while intelligent, might have been a mite overprotective, feeling that Felix could learn just fine from her. That makes your character grow up in a world of adults instead of being surrounded by children and it's a good reason why he could have developped to become serious and reserved.
One thing you may want to consider was the stance Felix's mother had toward his joining the army. Imagine beig the wife of a carreer soldier leaving for devastating conflicts that occasionally raise the body count in the billions. Maybe she was proud of that, but it could have had ranged just as much in other direction, such as Felix leaving without her approval to having his family divorce because the father was rarely home and the mother couldn't take it (hooking up with another guy, perhaps, which could have alienated your character and have his side more with his father - perhaps a strong motivation for joining the army at all... hey, maybe he wouldn't have gotten along with his mother's boyfriend ~_^ ).
Switching to a Yamataian's body in this case could have been something related to father hero-worship to merely going for a practical upgrade so Felix would be able to navigate zero-g passageway in nekovalkyrja-intended vessels or the like.
Right now, I feel you have a rather strong entry (I do recommend splitting your history in two paragraphs to air it up a bit). Do think about what I mentioned in the above and preferably outward from there : it will certainly add dept to think of your character beyond the "I'm serious and reserved" and "My father joined the SA, so, I joined too" once you get in an actual roleplaying thread.
Also, since you are new to the site and that your character has been acquainted with the Star Army for a good part of his life, make sure you check out the following :
- Star Army general info :
https://stararmy.com/org/stararmy/index.html
Skim over it. All that is info your character is likely to know... with added emphasis in here -->
https://stararmy.com/org/stararmy/military_law.html
Pay close attention to it, especially 'military courtesy', since this is a roleplay and you'll have to talk/interact with others a lot.
You'll be piloting a Phalanx or a Super Phalanx, so, do check 'em out as well. -->
https://stararmy.com/starships/phoenix/s ... alanx.html