From Manga Up:
“My best friend is the only one who has my spare keys, but for some reason, his little sister always sneaks into my room.” Ooboshi Akiteru is a high school boy who is the very definition of ordinary. He leads an efficient life while being content with his unmemorable existence until his days are completely changed by Kohinata Iroha, the younger sister of his only best friend, Kohinata Ozuma. She pesters Akiteru daily to the point he finds himself caught up in all kinds of troublesome situations. What’s more, he meets other girls who also have attitudes that are hard to deal with!