The Chaser

(from ebookjapan):

It was the early 1950s. There were no weekly manga magazines yet...

There was a mangaka who had already become the star of the age, Osamu Tezuka, the "God of Manga," who had been challenging him unnoticed! Koichi Kaitoku. He is a moderately popular mangaka with three serials in monthly magazines. Kaitoku is the same age as Osamu Tezuka.

On the surface, Kaitoku criticizes Tezuka, saying, "Tezuka draws a lot of boring manga," but secretly collects Tezuka's manga behind his back. When he hears Tezuka is doing something, he imitates it, and when he hears Tezuka is doing this, he tries it. This is the story of the struggles of Koichi Kaitoku, a man who "selfishly sees Osamu Tezuka as his rival!"