The Ideal Sponger Life manga volume 15 features story by Tsunehiko Watanabe and art by Neko Hinotsuki.

After navigating the succession dispute within the Twin Kingdoms, Zenjiro's visit home is unfortunately short-lived. He swiftly returns abroad with a gift from Queen Aura to Prince Francesco—marbles which carry incredible value in the arts of enchantment. Speaking with the man, he learns of a new revelation that could change the fate of the entire world! Not long after, Princess Freya visits the Kingdoms to request a magical item of her own. What could a northern princess from the realm of technology and progress want from the enchanters of Sharou?