Inou-Battle wa Nichijou-kei no Naka de, Charlotte Recommendations
Same super-power wielding students. The difference is that in charlotte, they have a organization where they gather all the teenagers with supers powers while in inou-battle they are already in a club before they "awaken" theirs.
Both have a student group that have superpowers that will come together in some kind of club
Both anime take place in a world where adolescence can mysteriously develop unique powers.
Both are about humans gaining superpowers. The main casts are both teenagers who have to keep their secret a secret. Also of one member their (almost) useless and imperfect abilities turn out to be one of the strongest!
High Schoolers with unbelievable Super Powers, Romance involve(InoBato isn't that romantic though :c). Charlotte isn't a harem anime but InoBato seems to be, I don't know why it doesn't have the harem genre. Both Animes Are Really Enjoyable c: