The Hour of Lambda

(from ebookjapan):

The betrayal of the man she loves awakens the mark of the devil - the Λ (lambda) birthmark! Mari, who has a "Λ" birthmark on her arm, works as a servant at the Kaibara Zaibatsu's mansion and is sent to school. Her boyfriend Kaji, a lawyer who frequents the mansion, is her emotional support. One day, Kaji brings Ayako, the niece of General Kaibara, who has been missing. When Ayako shows up, Mari's happy days are over... An innocent soul, exposed to betrayal and lust in the glamorous world of society, is transformed into a demon! The cruel, pathetic, and brilliant mystery of Mari, who became the avenging godchild!

Note: Was serialized as two parts: Part 1 in *Jotomo*, 1977, Part 2 in *Petit Seven*, 1979.