Onii-chan no Koto Nanka Zenzen Suki ja Nain da Kara ne!! - Vol. 1 Ch. 2 - Imouto-chan's Secrets and the Brother Back Then

[MangaDex]

 

[Jinyo]

"Adopted"
And in to the trash it goes.

 

[BakedBanana]

Not actual siblings? The author is a coward but at least he threw that info out early.