Heart Gear manga volume 6 features story and art by Tsuyoshi Takaki.

Roue, Chrome, and Rock have been taken in by Heaven Land's retrieval team, the Donkeys. They seem friendly enough, but Chrome isn't quite ready to let his guard down yet. The group decides to take the shortest route to Heaven Land, only to be attacked by a massive underwater creature! The Donkeys entrust Chrome with a weapon of massive firepower, but will it be enough to take down the creature and save them all?