This game is so far not very much like Hakuoki/Demon's Bond, aside from the historical theme. There's no sense of overarching inevitable tragedy and the romance happens *much* sooner. Like, the flirting starts nearly right away.

Anyway, here's the physicist/ninja:
https://ikemensengoku.fandom.com/wiki/Sasuke_Sarutobi

ETA: And here's a trailer for his route:
https://www.youtube.com/watch?v=v_PTVD5m-XE

In routes where you're not dating him he's still a good friend from the beginning.