LOVE COME MANGA NI HAITTE SHIMATTA NODE, OSHI NO MAKE HEROINE WO ZENRYOKU DE SHIAWASE NI SURU

I was sent into the world of a popular rom-com manga, and into the body of the male lead's best friend. Now I have the chance to make my dream come true: to make Sei-chan, the losing girl of the manga, happy! "I can give you all the happiness you deserve, so please go out with me." "Wait a minute! Are you serious?" (Source: Kadokawa, translated) — Description from AniList community (anilist.co).