Shounen ga Otona ni Natta Natsu – Episode 4 (RAW)

Protagonist Ryuki Kirishima experiences a shocking realization: for the past four years, his adored older sister Reiko has refused to let him enter her room, sparking deep suspicion. Determined for answers, he steels himself and opens the door—uncovering a truth that exposes Reiko's hidden true nature. As layers of deviation and secrecy peel away, Ryuki finds himself increasingly aware and entangled in the chaos, feeling an unexpected sense of liberation amid the escalating taboo acts. His emotions surge to the point of no return, with passion overwhelming any hesitation. The intimate secrets shared only between the two siblings prove unbreakable, destined to persist even into adulthood. This revelation reframes Ryuki's earlier encounters with Kiriru-sama, highlighting Reiko's central role in his awakening. The episode culminates in profound, boundary-shattering encounters that solidify his transition from boyhood innocence to full manhood, wrapped in the heat of summer and irreversible familial desire. A poignant yet intensely erotic close to the series, teasing the eternal nature of their clandestine bond.