Tenohira no Hoshi – Risa’s Route
Risa, a runaway girl, shows up at the home of a struggling university assistant professor.
She says things like, “I can’t wear underwear today,” or “I can’t eat today,” and even casually strips in public without a care. The protagonist is constantly thrown off by her bizarre behavior, but he gradually finds himself drawn to her radiant, almost blinding presence.

Kokoro no Kokoro – The Twins’ Route
After starting university, the protagonist ends up living under the same roof as his two childhood friends—his older cousins.
There’s Ritsuki-nee, who’s a little naughty, and Itsuki-nee, who’s more domestic. Caught between the two, the protagonist’s heart is in turmoil. But lately, something seems off about the twins. Are they hiding something…?

Yuki no Hane – Kohane’s Route
After the death of her fiancé, the protagonist takes in his younger sister, Kohane, and the two live together as siblings.
Kohane, despite being of age, shows no interest in boys and remains clingy and dependent. But lately, she’s started to resemble his dead fiancée more and more…

[Translated from dlsite]