Complex sentence: His debut work "New Treasure Island" was released in 1947 as a comic book through Ikuei Publishing and sold 400,000 copies, though it was the popularity of Tezuka's Astro Boy, Metropolis, and Jungle Emperor manga that would come to define the media.
Split into simpler sentences: His debut work "New Treasure Island" was released 1947 as comic book through Ikuei Publishing and sold 400,000 copies. Though it was the popularity of Tezuka's Astro Boy, Metropolis, and Jungle Emperor manga that would come define the media.