The battles of the animal kingdom

June 12th is Strongest King Encyclopedia Day 最強王図鑑の日 (Saikyō-ō zukan

). The anniversary was created by Gakken, the Tokyo‑based publisher known for its wide range of educational books. The date marks the first publication of the very first volume in the series, Animal Strongest King Encyclopedia, released on June 12th, 2015. 

The Strongest King Encyclopedia series takes animals, dinosaurs, insects, mythical beings, and even extinct creatures, and places them into tournament‑style battles. Each book selects 24 contenders and follows them through rounds, first battles, quarterfinals, semifinals, and a final showdown, to determine the “strongest king” of that category. The appeal lies in its mix of real biological traits, bold illustrations, and the pure fun of imagining dream matchups like an African elephant versus a polar bear.

Over the years, the series has expanded into many themed volumes and has surpassed four million copies in total. Gakken established this anniversary to celebrate the creativity behind the books and to share their excitement with even more readers.