Heart Mark Oome.

In Episode 2, Asahi — a girl who secretly has strong feelings for Yuu — discovers that his step-sister Reika is actually a popular erotic manga artist. Without hesitation, Asahi becomes Reika’s assistant to get closer to Yuu. Driven by jealousy and pent-up lust after seeing the lewd atmosphere, Asahi transforms into a hypersexual mode just like Reika. She aggressively seduces and attacks Yuu with intense sex. Meanwhile, Reika finds out what happened and gets involved, turning the situation into a competitive, non-stop threesome where Yuu is relentlessly drained and squeezed between the two horny women.