Cuckolder and Cuckold

Ryouta is in love with his brother's girlfriend, Yuna. She's been his unrequited crush ever since high school, but now his player of a brother decided to make Yuna his. Ryouta can't bear the thought of the innocent Yuna being toyed with, and he decides to steal her first time instead! They get together under the pretense of "training", but what...