Shitsuren shita node VTuber Hajimetara Toshiue no Oneesan ni Motemashita

Yuki Himemura is shocked to find out that the club senpai he's had a crush on got a boyfriend, so he decides to become a VTuber—something both his senpai and he have always liked—and uses up his savings to assemble his equipment. He gets his virtual character designed only to discover that it's a 3D model of a cute girl, and he unintentionally becomes a girl!

(Source: Akita Shoten, translated)