The Side Character Who Thought He Was the Protagonist Mistook the Real Hero for a Side Character and Accidentally Won Everything

Jibun no koto o Shujinkou da to Shinjite Yamanai Fumidai ga, Shujinkou o Fumidai da to Kanchigai Shite, Yuushou Shiteshimau Ohanashi desu

自分の事を主人公だと信じてやまない踏み台が、主人公を踏み台だと勘違いして、優勝してしまうお話です