She is making a logical mistake. Her point is only valid for a singular mother. They could have the same father without any problem...
And I am only the second one to notice.
@Lum1N0us i hate the anime so much for downgrading the character to the point i dont want to watch it beyond 1st episode.
@chipusu as far as i remember, i never seen a chapter keiki knowing that mizuha is not blood related sibling
@Aricitic well, according here https://hensuki.fandom.com/wiki/Mizuha_Kiryuu the light novel said she is not blood-related. that means a complete adoptive one, not different mother
now no wall holding back Keiki for no nut november with Mizuha
Wait, this can’t be the first time they’ve questioned a five month age gap right? Or how about anyone around them? I mean did everyone just see their birthdays and thought “yeah. That’s normal”?