Mai Friend!

A house renovation is the excuse; a summer under one roof with his estranged little sister is the actual reason he can't stop sweating. When three of her friends turn up uninvited and unannounced, what was supposed to be an awkward reunion turns into something else entirely.

The setup: separated by their parents' divorce since junior high, the protagonist and his sister have barely spoken beyond one New Year's visit. A sudden house rebuild forces him to move in with his mother and sister for the summer, and their mother conveniently leaves on a business trip almost immediately. Just as he starts entertaining the obvious thought, three girls he's never met show up saying they're staying too, turning a quiet family reunion into a house full of people he has no idea how to act around.

It plays as a visual novel: read, click through the growing cast of housemates, and steer things toward one of several endings depending on who you end up closest to. The protagonist's name is fixed and can't be changed, for whatever that's worth.