Since going into the tag for the game I saw a regrettable amount of Ima hate already, I must take up arms to defend my boy
Like, yeah, we all know about the siscon bit. Feel however you want about that, but there's clearly gonna be more to his character as well (even if that thing is definitely gonna be there too). Thus I present to you;
Things I like about Ima that aren't about his sister:
His design is very pretty and adorable, I love his hairstyle and his eyes are gorgeous
As a bit younger than the others, he's very polite to his seniors, and seems to refer to them as 'miss' and 'mister' (mister Sumino, mister Aotsuki)
cute!
However
in contrast to his cute appearance and polite exterior, he's very cold and jaded, and says weird/gross things without thinking/caring about it
Said appearance/personality gap is also a charm point for him
Both him and Kako (ok, I know I said I wouldn't mention her but bear with me) seem to have been through a lot from early childhood, which probably explains some of his indifference to the suffering of others, and his desire to protect that which he cares about - he's used to focusing his efforts and protecting himself
Just like his introductory trailer dialogue, he doesn't hesitate to do what it takes to protect that which is important to him - no matter what it is - likely because he's used to fighting for himself, without having anyone look out for him
Despite most of his dialogue being about Kako, he also seems very perceptive to his surroundings, and makes some clever comments about their circumstance
(I know the comment about the surgery gets pivoted to him defending Kako, but again, bear with me)
He seems almost used to dealing with extreme situations and takes them in a stride - like his nonchalant reaction to being kidnapped
Again, I know I promised to not talk about Kako - but they both seem to share an interest in mystery solving
At least that's the feeling I get, from how they seem to be speculating and suspecting about everyone's shared background in the TRC
tl;dr: Even aside from his protectiveness of Kako, Ima has an impeccable character design, promises some funny dialogue (even the stuff about Kako sometimes), and, shockingly, an actual personality - even if it's largely molded by his implied life circumstance thus far. Which was already elaborated a surprising amount in the demo, and hopefully much more in the full game itself.