Love Come Manga ni Haitte Shimatta node, Oshi no Make Heroine wo Zenryoku de Shiawase ni Suru

A man finds himself transported into the setting of a well-known romantic comedy manga, inhabiting the body of the male protagonist's close friend. He sees this as an opportunity to fulfill his wish of bringing happiness to Sei-chan, the girl who loses in the original story. He proposes to her, saying he can offer her the happiness she deserves. She reacts with surprise and questions his sincerity.