Substitute Girlfriend ~I'll Become a Slutty Gal to Protect My Best Friend!~

"Wait, Sui-chan... You got a boyfriend!?" - I received a shocking confession from my best friend, Sumi Mizuki, that she had gotten a boyfriend. - And to top it off, her partner was none other than the popular and handsome Matsui Tatsumi at our school. - At first, I was celebrating Sui-chan's relationship, as she was my only friend at school. - However, I gradually began to sense that her appearance and behavior were changing for the worse.