Jack Knife Dragon, originally named Findar the 100th but commonly called Jack, is a dragon from Dragon World. He serves as the dedicated buddy monster to Tasuku Ryuenji and is a prominent member of the Buddy Police. Jack shares an exceptionally strong bond with Tasuku, whom he considers family, investing significant trust in him and granting him the ability to fly. He typically maintains his large, full size in daily life despite possessing the capability to shrink. Physically, Jack is a towering green-scaled bipedal dragon, taller than Drum Bunker Dragon. His initial design features a helmet with a retractable blade, black armor adorned with grey edges and red highlights, and four-fingered hands. His appearance undergoes significant evolution: - As **Star Guardian, Jackknife**, he adopts futuristic armor with a neon-blue helmet blade, brighter green scales, a yellow underbelly, and reduced scale patterns. - In **Radiant Guardian, Jackknife "Aster"**, his scales turn blue, covered by golden futuristic armor including a fully enclosing gold helmet, with glowing streamlined accents. - His **Star Dragoner** state merges Dragon World and Star Dragon World elements, keeping his green coloration while integrating advanced armor and weaponry. Jack's personality blends seriousness, protectiveness, and a strong sense of justice. He demonstrates eagerness in battle without arrogance, prioritizing the safety of others, especially Tasuku. Their profound bond faces a severe test when Tasuku, under Disaster's influence, temporarily transforms him into the mindless weapon "Goldritter." Jack actively works to restore Tasuku's sanity and forgives him afterward. He dislikes transforming into his SD form but does so reluctantly to support Tasuku emotionally, gradually becoming more accepting of it. A rare break in his serious demeanor occurs when he laughs at a criminal's core gadget placement. Later, he mentors younger monsters like Bal Dragon, showing patience and tolerance. His story begins in Season 1, fighting alongside Tasuku as a Buddy Police officer. Captured and freed from Azi Dahaka's arena, he joins Team Balle Du Solle to rescue Tasuku from Disaster. During the Gaen Cup finale, Jack defeats Demios Sword Dragon and delivers the decisive blow returning Tasuku to normal. He later visits Tasuku in the hospital, using his SD form to help him overcome guilt and rebuild their bond. In Season 2 (Hundred), Jack trains with Armordeity Dynamis and evolves into Star Guardian, Jackknife after Tasuku embraces Star Dragon World. Taken to Star Dragon World's future, he evolves further into Radiant Guardian, Jackknife "Aster" using Gargantua Punisher. By Season 3 (Triple D), he achieves his Star Dragoner form to harness the power of Star Dragon World itself, interacting with Bal Dragon at Aibo Academy. Jack also participates in the Gao Genuine Gameface Tournament featured in "All-Star Fight." His combat abilities involve expending gauge to summon alternate versions of himself onto the field, with specific effects requiring positioning in left or right monster areas, embodying the "Jackknife" archetype's namesake ability to function as multiple monsters simultaneously.