Like the title says, I'm looking for any story where the MC lives a double life. Preferably something in a school setting where the MC is a normal student with friends and normal kid issues during the day and some kind of action/shounen battle character at night. No real preference too genre. But if the MC's lives overlap every now and then in the weirdest ways that would be great.
Off the top of my head https://www.novelupdates.com/series/i-came-back-but-the-world-is-still-a-fantasy/ is what I can think of. Might think of a few more once I get the CPU warmed up a bit.
Maybe The Undetectable Strongest Job: Rule Breaker? Idk, its a typical isekai. On one of the arcs, is what you described where he's a student but also an assassin, but not the main point of the story tho.
Maybe something like: Shadow Hero’s Everyday Life The Strongest Dull Prince’s Secret Battle for the Throne Hazure Skill “Kage ga Usui” o Motsu Guild Shokuin ga, Jitsuha Densetsu no Ansatsusha The Gloomy Me in Class is Actually the Vocalist of a Very Popular Band The Best Assassin, Incarnated into a Different World’s Aristocrat To be a Power in the Shadow! Baito de Aku no Soshiki