This is a special collaboration work featuring S1's exclusive G-cup beauty, Mai Tsubasa, and Madonna's 20th anniversary! Mai Tsubasa isn't my real sister. She's my stepmother's daughter from her previous marriage. After my parents fell ill, Mai Tsubasa became like a mother to me. As we spent more time together, I gradually developed feelings for her. One day, I invited my classmate Yui home for a cultural festival meeting. Yui seemed interested in Mai Tsubasa from the moment they met, and she started coming to our house frequently after that...