Itoko No Onee-Chan Ni Amaechau?

***A heart-pounding new life together with my "big sis cousin"!?*** Masato Ooizumi just entered high school and he finds himself staying with a relative. Living there is his "big sister cousin" who's being way too close with him!? A slightly naughty, living together romcom begins under one roof!! (Source: Ultra Jump) --- Serialization published in Ultra Jump starting in the June 2024 issue, released on May 17th, 2024.