Sekai's role is almost the same as in the anime. The big difference is that she is far more forward about her feelings for Makoto, but ultimately accepts Makoto loving Kotohona more then her. She even shows a willingness to remain friends with Makoto and accepts being dumped with a smile.
Another -Misaki & Sakakibara
carteles school days anime sekai kotonoha yandere desmotivaciones
List of School Days episodes - Wikipedia, the free encyclopedia
Day 20 ~ Most annoying character ever: Makoto from School days. Not only did I dislike the anime, Makoto just got on my nerves. I couldn't continue watching this anime and left it at episode four.
Here a different side of Makoto is shown as his motives are based more on love than on desire. His role has similarities to that of the anime; however, in the manga he does love Kotohona and he feels guilty about cheating on her with Sekai.
Her Manga version is mostly the same as in the anime with the difference is that she accepts Makoto loving Kotohona more and even accepts being dumped by Makoto. However she becomes insane after Makoto is critically wounded by Kotonoha who tried to murder Sekai and kills her a week later.