This is one of those manga with the "obviously OP main lead, but with very low self-esteem" kind of trope, which is definitely a cliche in the manga world.
You got this male MC, which is clearly your "unusual" high school student, where he was shown training with the military, and can speak multiple languages. Yet somehow, he chooses to just "stay low" in school, since he doesn't want to stand out, which is an absolute cliche.
But then he was introduced with the main female lead, which was a young Russian girl that was very shy with people, and can't speak other languages except Russian. She was happy with their meeting, because now she can communicate with someone with her age.
Even after their "fated meeting", he still trying really hard to keep his facade up during school, which only brings more trouble to the girl, since he totally ignored her, despite she literally begs for his help.
I seriously not enjoying the story with this kind of shit MC, where he's nothing more than a goddamn closet-pervert who tries really hard to be a "normal guy" + being passive all the time in public, while being an overly-possessive simp when he's alone with the girl...