Who is Koizumi Akako in Conan?

It's a character in The Magic Fight, a cartoon featuring Kidd, which has been animated for one episode.

Koizumi Akako, Kidd's classmate, comes from a witchcraft family and is a witch with superb witchcraft. The second heroine in Magic Fight fought a big battle in Detective Conan OVA "Conan vs Kid vs Yaiba!" There is also the feature "Detective! Kudou Shinichi VS Blackfield Haidong appeared.

A beautiful girl, all the boys in the class like her except Kuaidou, but Hiroko just likes Kuaidou. Hiroko knew the true identity of Kuaidou and helped him hide it several times. He is Qing Zi's number one rival in love.

If you want to know about Koizumi Akako, you can read the comic book Magic Wars.