Responses
it's a poetic story on many levels. i suppose people are icked because he kepy calling him nii-san/brother, and since it's a formality in Japanese language that isn't really shared in many other cultures... or who knows. for me it's as if they aren't related at all. but they have another type of stronger bond which can indeed be beautiful

Sister played Cupid from 6 feet under — as her Sakura tree bloomed for the first time, a forbidden love she blessed from the grave officially surfaced. As Yuki and his Nii-san both walk hand by hand to overcome their grief and guilt, they recognise in the other their only hope and reason to keep on living. Yuki’s quest for happiness has just began. The future is bright.
Honestly, Idk why everyone is so salty about it. They’re not related by blood, and there’s something so poetic about two people grieving the same person together and finding in the other the force to keep going.