It Was Obviously Pure Love, but Why Did It Gradually Become a Shura Field?

During that vacation, Su Chen met a beautiful older sister who suddenly moved in next door, and started a semi-cohabitation life together throughout the summer vacation. A cool young lady who doesn't like to talk has been transferred to the class, and their daily lunch break has become a unique world for the two of them. It was another holiday, and the lovely sister who came to stay with his sister's friend occupied his room and stayed with her day and night for two whole months. Why, it felt like I was trapped in some very weird atmosphere with them. It obviously started out as pure love, but why did it gradually develop into a Shura field?