Jibun no Koto wo Shujinkou dato Shinjite Yamanai Fumidai ga, Shujinkou wo Fumidai dato Kanchigai shite, Yuushou Shiteshimau Ohanashi desu @comic

A certain high school boy who admired protagonists from manga and games died while saving a child. At that moment, God appeared and said he would reincarnate him as the protagonist in a visual novel game world. The boy trembled with joy, but that was God's big lie. His reincarnation destination was actually as a pathetically weak stepping-stone character! However, his extraordinary, abnormal efforts based on his delusion of being the protagonist began to drastically rewrite the status of this weak character! This changed the original course of the story, saved beautiful girls, and eventually even saved the world...? The heroic tale of a misunderstanding man who saves the world through sheer conviction!