The Boy Who Ruled the Monsters: Volume 5

"Now that he has secured one more monster—the Demon Lord Alshunna—as a companion, Sol is free to focus on restoring the All Dragon to her prime state. He chooses to go for her wings first, which are sealed inside Abyss—a massive dungeon that no one has ever returned from. One of Sol’s dreams has always been to conquer a dungeon, so he marches in, accompanied by both monsters of legend and companions decked in brand-new gear. Unfortunately, Abyss is protected by Country Eater, a boss that once obliterated seven countries within a month, and Country Eater won’t be their only obstacle in returning home! What truths will the greatest supporter and his party find as they delve into the heart of the earth in volume five of this ultimate fantasy?!"

[From J-Novel Club]