Nanami no 623 Nanami's "Six-Two-Three"

Synopsis

Makoto Harada, a bullied boy who likes fighting games, happens to become privy to a secret about the student council president, Nanami Fujisaki. Makoto threatens Nanami until she promises to participate in a fighting game tournament, but she is a complete noob!! Makoto teaches Nanami the inner mysteries of fighting games...!? (Source: Shogakukan, translated)