From Bulbapedia, the community-driven Pokémon encyclopedia.
How I Became a Pokémon Card (Japanese: ポケモンカードになったワケ Pokémon Card Ni Natta Wake) is a manga created by 姫野かげまる Kagemaru Himeno, who is also an artist for the TCG. While the manga includes some reoccuring characters, each chapter is mainly a standalone story featuring one Pokémon, such as Dratini or Jolteon. At some point within each story an image of an actual Pokémon card is shown, the stories expand on the image that appears on the card and tells about what the Pokémon is doing in the picture or how it got there.
A special Pokémon card is included with each book. Each promo card, as well as all the cards featured in each chapter, are originally illustrated by Himeno herself.