Takumi Disappointment

I would maybe focus on utilizing his Kagami Mochi+ debuffs and just have him as a team debuffer for your team! Although he is -ATK his speed is still decent so with an A slot skill like Life and Death 3 or Fury 3 and a Speed enhancement on his mochi you could run Threaten Attack 3 or the Attack Smoke Seal and Windsweep 3 as his B skill so that he can debuff melee units that have Distant Counter but will be slower than him before finishing them off with other units.

NY!Takumi has the most powerful base dagger in the game; only beaten out by a forged Deathly Dagger. In addition, by forging for speed you can get a field of -7/-7 defensive debuffs out pretty fast.

I run a Summer Frederick with Seal Atk/Spd and Threaten Attack atop a forged Seashell+, so it would be like that but with the +1 cooldown reduction for an extra little offensive burst. You could run Seal Speed in B and Threaten Atk in C; so that he debuffs everything.

I'd be saying that Fury or a Blow skill is probably best, I run Armored Blow on my Frederick. Add on Moonbow and he'll be hitting hard and debuffing more.

First off, you can always fix his attack with seals or skills. Speed is important but I got +ATK-spd and my Mochimi is still devastating. I think Fury with Desperation or L&D would all be great options. Appreciate his art, you got thru colourless hell for him:)