Mangetsu no Yoru, Ikemen Oyako ni Deaimashita

Naruse Shouta, a struggling theater troupe member, encounters a mysterious father and son under the light of a full moon. The father, Hase Naoki, a university lecturer, shares a startling secret about his son, Yuzuki...?! (Source: Koubunsha, translated) Note: Includes one extra chapter.