Saikin, Imōto no Yōsu ga Chotto Okaishiin Da Ga.

When a sudden, tragic accident claims his mother's life, Yuuya finds his world upended in more ways than one. His mother's dying wish introduces him to Mitsuki, a beautiful girl who is now his stepsister. But this new family dynamic is complicated by a peculiar and persistent problem: a spectral presence has attached itself to Mitsuki, claiming to be the ghost of a young girl with an unfulfilled longing. This ethereal roommate, Hiyori, informs Mitsuki that she must help her find true love before she can finally move on. The only catch? Hiyori can only act through Mitsuki, leading to increasingly awkward and often hilarious situations as Yuuya navigates the challenges of a new sibling relationship, a house haunted by an insistent spirit, and the growing, undeniable strangeness of his sister's behavior.

✦ AI-drafted summary