Ooh, maybe he has a meter that charges over time and empties whenever he swings his sword. If the meter is fully charged, all his attacks are powered up somehow. That would really fit his flavor of "striking decisively at the right moment", and would organically enforce the no combo aspect.
Here's a v3 of my sketch incorporating that
A: Sword Slash. medium speed, medium range vertical slash. Primary anti-air.
When charged: Faster speed
B: Divide and Conquer. Horizontal slash. Slower than the A attack, but with longer range.
When charged: if it hits or is blocked it automatically follows up with a second slash for another damage (or another chip)
C: Clockwork Shield. If you catch an attack with it: damage is prevented and a Clockwork soldier appears in front of Oni. The next attack that would hit Oni is blocked by the soldier instead, which then breaks. The soldier also breaks the next time Oni attempts a special move. If the initial parry whiffs it's highly punishable
When charged: N/A
S: Final Authority. Slow slash that does 2 damage (similar speed as Grave's C). Unthrowable, but can be interrupted by faster attacks.
When charged: Unblockable
jA: Sword slash. Holding a direction moves him a little bit in that direction (helps with air mobility to avoid projectiles). Does not combo if used as a jump-in
When charged: Longer range and higher priority
jB: Spirit Fire. Oni hangs in the air and fires a slow moving spirit projectile at a sharp downward angle
When charged: Projectile knocks down
jC: General's Hammer. Slow overhead slash that hits almost 180 degrees in front. Knocks down
When charged: 1 HP of armor
jS: Clockwork Formation. Summons 3 Clockwork soldiers. Every time Oni attacks, a soldier attacks as well for 1 damage. Soldiers do no chip though, so a blocked or whiffed attack wastes a soldier for nothing
When charged: N/A
Roughly Midori's walking and jumping speed
Poor throws (short range, no KD)
Sword meter charges at about the same rate as DeGrey's ghost