A humanoid-type Gear that once was under Justice's control during the Crusades, Testament is the adopted child of Kliff Undersn. Able to wield blood magic and a crimson scythe in battle, Testament fights alongside their succubus familiar, EXE Beast.

Sin Kiske, the forbidden child of a human and a magically crafted biological weapon called a Gear, lives in a world where magic has replaced science, and scars from the Gear rebellion remain. Attending his parents’ taboo-breaking wedding, he encounters a mysterious girl with deep hatred for Gears, and their fateful meeting threatens to upend the world once again.<br><br>
(Source: Crunchyroll)