Jenius stands among the original Seven Knights, legendary warriors chosen by the goddess Serrass to oppose the evil goddess Nestra and her cult, Physis. His spirit bonds with protagonist Nemo through Succession - a process allowing modern individuals to channel ancient heroes' powers via special cards. Unlike other Successors, Nemo initially cannot hear Jenius's voice or identify him, marking their connection as unusual.

Renowned for exceptional strategic intelligence and analytical prowess, Jenius exhibits a calm, collected demeanor and strong leadership on the battlefield, often formulating decisive tactics. His inventive nature manifests in advanced combat gadgets, including a customized gun used alongside his sword.

Central to Jenius's legacy is the "Legis Breaker," an immense energy cannon. This weapon becomes key to Nemo's abilities, manifesting through a gauntlet grappling hook connected to a blade that transforms into the Legis Breaker during combat. Jenius's spirit actively guides Nemo's growth towards mastering this weapon despite their fragmented communication.

Jenius's backstory intertwines with Nemo's origins. Nemo is later revealed as a homunculus created by Physis member Amis Germain, intended to become the "Son of Destruction" destined to awaken the God of Destruction. Jenius's spirit inspired this homunculus to reject its fate, leading it to escape and assume the identity of a human boy named Nemo after the original Nemo sacrificed himself to save it. This act links Jenius to Nemo's fabricated memories and identity.

In the climax, Jenius's spirit fully manifests to aid Nemo against Sophitia, Physis's true leader. They combine powers to recreate the "Book of Time," sealing Sophitia and the dark forces within. This act extinguishes Jenius's soul completely, leaving Nemo without his Succession powers but free from his homunculus destiny. Jenius's sacrifice underscores his role as a guardian committed to protecting the world.