General Onimaru is Quince's top military man. You can think of him like Sun Tzu in that he's a master of the art of war. He is known for his strategic planning, tactical maneuvers, use of terrain to his advantage, his ability to discipline an army, and his ability to know the enemy.
Onimaru is actually an outsider to Flagstone, though he's won many battles in foreign lands and at least one on Flagstone soil against the former regime. Grave was just a boy then, and he lost his father that day. Onimaru claimed the Stormborne family sword as a war-prize, and were it not for the intervention of Mistress Persephone, Grave would never have received his family heirloom.
Many years later, Quince was able to recruit the General. There, Onimaru raised an army and due to his harsh style, the troops called him the Flagstone Enforcer. He also investigated unorthodox forms of military force, including the use of wild elephants and an experimental program to create clockwork soldiers with the help of the then-head of Flagstone Research & Development: Max Geiger.
In a fighting game, Onimaru won't rely on combos. Just the right strike at just the right time is more his style. All his moves in his (still in-development) Yomi deck are actually "Can't Combo" moves, and yet he's still a fearsome opponent.
In Flash Duel, he has one of the most interesting abilities in the game, Clockwork Soldier:
The Clockwork Soldier greatly restricts the opponent's movement. It puts the squeeze on them, letting Onimaru close the distance to them one way or another. This opens up even more potential interactions in the 2v2 and Dragon Raid modes.
In Puzzle Strike, Onimaru shows his versatility with Wartime Tactics:
This lets him reveal a puzzle chip from his hand, then get a one-time use of any other puzzle chip in the bank, as long as it costs the same or less as the revealed chip. Onimaru's tactics are so honed that this gives him access to a wide variety of effects immediately, without waiting the usual one or two turns to draw them.
General Onimaru is a formidable foe to anyone who would threaten Flagstone or its right to rule. That goes double for outlaw barristers and mutant stone golems who would sow the seeds of dissent with their illegal Fantasy Strike tournament.
Next time we'll meet Troq, a lowly foot-soldier in the Flagstone army.