Takumi

Weapon: Spendthrift Bow+ (+SPD)

Assist: Draw Back / Flexible

Special: Moonbow / Deadeye

Passive A: Close Foil / Atk/Spd Solo

Passive B: Lull Atk/Spd / Quick Riposte

Passive C: Pulse Smoke / Atk Smoke

Sacred Seal: Spd/Res Solo / Quick Riposte

• Spendthrift Bow breathes some new life into Takumi, allowing him to run a defensive set which, when combined with Lull Atk in his B slot, fully debuffs his opponent's Attack by -10 while increasing his own Attack by 7. This grants him additional survivability in combat so he can be utilized as a tank.
• Spd/Res Solo in his Seal slot and an appropriate Smoke skill in his C slot further enhances his survivability.
• You can try to run Quick Riposte in his B or Seal slot if you're worried about him getting outsped - even with a Spd boon, +Spd refine, Atk/Spd Solo, Lull Atk/Spd, and Spd/Res Solo, Takumi hits around 50 Speed, which barely competes with units like Summer Byleth. Therefore, it might be better to utilize Quick Riposte instead of Speed stacking, though it comes at the expense of reducing one of Takumi's survivability skills.
• If you want to go full Attack, that could work too - by running Lull Atk/Def in his B and Atk/Def Solo in his Seal, Takumi can do more damage and try to focus on taking his opponent out in a single hit.
• This set allows Takumi to compete in modes like Aether Raids due to stat stacking, despite being a now-mediocre launch unit.

Preferred IV: +SPD or +ATK / -HP

Weapon: Fujin Yumi+ (+EFF)

Assist: Draw Back / Flexible

Special: Deadeye / Moonbow  

Passive A: Sturdy Impact / Swift Sparrow / Death Blow

Passive B: Lull Spd/Def / Wings of Mercy

Passive C: Time's Pulse / Def Smoke

Sacred Seal: Quickened Pulse / Swift Sparrow / Death Blow

• If you really want to kill Shinon for Takumi to inherit Deadeye and Time's Pulse, we won't stop you.
• This set requires great sacrifice, but is probably Takumi's best bet when it comes to using Fujin Yumi in Aether Raids Defense, as Takumi is so laughably underused in most PvP these days that some players may genuinely forget what it does and be surprised by Takumi's sudden teleportation.
• Time's Pulse and Quickened Pulse work together (though you could give Takumi an ally or two with Infantry Pulse for a third charge and/or free up a skill slot) to give Deadeye a low cooldown, which allows Takumi to blow a small hole in units like Brave Dimitri or Brave Ike or anyone using a skill like Close Call. Will it be enough to kill them? Probably not, with Takumi's base 32 Attack, but it'll definitely hurt, especially if you buff his Attack with skills like Death Blow.
• Sturdy Impact or Mirror Impact is for Takumi's own survivability, forcing his opponents to one-shot him if they want to kill him in a single engagement.