Wincest?

kissxsis isn't incest.

Saikin, Imouto no Yousu ga Chotto Okashiinda ga is one that comes to mind, but it isnt really like kissxsis. maybe you'll like it. (I only watched the anime adaptation, not sure how the manga is)

Synopsis:
High school girl, Kanzaki Mitsuki, just got a new older brother when her mother remarries a fellow divorcée with a son. Soon after, her new step dad gets transferred overseas and her mother follows him there, leaving Mitsuki alone with her new step brother, Yuuya. Feeling abandoned by her mother, she stays distant from Yuuya, never really getting along very well with him nor even keeping a conversation with him.

However, one day, Mitsuki gets visited by an angel/ghost named Hiyori who takes over her body and tries to make sexual advancements towards Yuuya. Hiyori is the lost spirit of a girl who died but can’t reach the gates of heaven and reach eternal peace. To reach heaven, Hiyori puts a belt on Mitsuki called the TST that fills up every time Mitsuki feels sexual feelings from Yuuya, whether it be from going on a date, kissing or even sex. For every time it fills up, Hiyori gains a step on a bridge that connects her current situation and the literal gates of heaven. If she wants to get rid of the annoying Hiyori, Mitsuki has to make some bold and sexy moves against her own brother, even if he is just a step brother.

(Source: MangaHelpers)

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Boku wa Imouto ni Koi o Suru

It's a shoujo manga but holy gods it has TONS of sex in it. Mostly between Iku and her twin brother Yori. Very smutty.

>>2100809
Fuck off, just skip the last episode

Any incest manga of sisters rather than it always being with a brother?

>>2100805
Pick up Yosuga no sora OP you won't regret it.

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>>2100879
I know of four examples.

Shoujo Sect where two sisters fall in love and have sex.
https://myanimelist.net/anime/4473/Shoujo_Sect

Sono Hanabira ni Kuchizuke wo: New Gen
https://vndb.org/v16262
a visual novel with a pair of twins that become a couple. It has an English translation.

Kamitsure
https://vndb.org/v15731
a visual novel about a girl with a male alternate personality, because of this she's only interested in girls. One route is her sister's route

and
Color of White
https://vndb.org/v11899
a visual novel about two sisters who fall in love with each other but are too scared to confess because they're both afraid not only that the other won't be lesbian but that she won't fall in love with her own sister.