Chapter 1: The start of the journey

Imagine feeling pity for the protagonist as his best buddy revealed his true colors and steals his lover. Normally, it ends there as the Protagonist moves on and goes on his adventures through either sorrow or trying to become stronger and move on

But what if..... the person.... Becomes the NTR antagonist himself?

Disclaimer: This original idea is not mine. It was from another manga that will follow the similar motives to the series

There won't be any NTR.