it IS incest right??

Technically not, they're not biologically siblings. They became one because their parents remarried each other.

And neither of them saw the other as siblings, I'd say

Just to add: their parent's only remarried a few years ago...
and given the time when MC woke up her consciousness...they've been step siblings for just a few months. They're practically strangers, in my books.

But in the flashbacks they're children?? Like small kids, ain't no way they weren't raised as siblings. I need a timeline STAT

lmao, think about it this way. An adult gets reincarnated into the body of an ~8 who knows that her "brother" barely even views her as human (at least at the start) much less a sibling.
They've been step-siblings for years at this point but any real familial connection is disrupted by the age gap (she's like >30) and mentality of the brother

Wasn't she a teen when she died?

i totally forgot that, okay it's less strange now

i thought she was early twenties? in my mind, she's brushing 30 at this point, I could be wrong

hey, nvm, I checked the chapter one; she was in high school lol! my brain meshes a lot of stories together, i must be remembering a different one

Happens to me too,
But even if you add her age from her previous life to this one, it doesn't really happen frequently in these type of Manga. You can see she is just a teen even now.
It's like they always know the future but never grow up until the determined age
Don't know why tho

I know it seems like that because of the art style but they met when they were 10. She's 14-15 now, so like only 4-5 years or so. It's not short, but not that long.
But that's for the "game setting" Mai. The "current Mai" who is a transmigrator just woke up like a few months ago. She woke up around end of summer just before HS started.

The game-setting Mai maybe saw him as an older brother, but he's never seen her as a human, much less as sister. And the current Mai is well...a stranger entirely. The current Mai was a sick girl in HS...so you could say she's finally able to live HS like a normal teen.

Almost a year or so will transpire before "D"-day which is when he is supposed to kill his whole class.