The brother noticed his sister Aoi's suspicious behavior. When confronted, she admitted to practicing putting a condom on his penis. Since then, he has been helping Aoi practice putting on condoms, but leaving it erect is too painful. He asked Aoi for support in ejaculating. Unable to endure with just handjobs, he progressed to fellatio and vaginal sex. Eventually, they agreed that 'inserting only the first 3 cm does not count as sex' and began repeatedly having glans sex. Soon, inserting only the glans became unsatisfying, and both of them started wanting to penetrate all the way into the vagina.
