Machina

Start with Stunning Slash (LD) to drop [Spiral's Lynchpin] as it gives Machina 2 more HP attacks after he attacks or after an enemy take a turn with the debuff.
Free skill usually goes to Awakening (S1) for free damage and to get Furious Blades+. You may choose to AA instead for the buffs as there is very little risk of running out of skills when played well due to his special HP commands.
With BT+ 3/3:
- use can BT Finisher then spam Furious Blades (Burst) in Burst phase
  - Ideally go into BT phase with 3 stacks of BT effect with 6T or 7T remaining to cover the entire phase.
  - Similarly with Force Time in an aggressive team (launches and linked attackers paired with Machina) opt to enter BT phase with 6T left in Force Time.
- You can use BT finisher before/during Force Time with full duration of [Spiral's Lynchpin] and EX buff up if enemies have high speed/turn rate or lots of threshold attacks for Machina to take advantage of. This way Machina counters and attacks raising his own (or other off-turn) FR conditions while pumping out damage.
- To get 3 stacks of his BT Effect quickly, set up a launch for Machina to act in or let the enemies take turns with his [Spiral's Lynchpin] up as both these will grant stacks.
Cyclone Drive (S2) has instaBREAK which can help in a pinch if you can't shave quickly enough and lack the mitigation to deal with the oncoming damage.
Guardian Blades (EX) provides him his EX buff which provides him good stats and the counter from it has an HP attack if he's hit with BRV attacks.
Beyond the Atonement (FR) boosts melee attacks HP damage and limit by a whopping 50% during Force Time! It also asks for:
- Abnormal turn rate (15%). This asks for high turn rate, instant turn rate or even low turn rate that some moves already have. Some unique buffs like Lunafreya's Quick Prayer or Cater's base Call Ability can offer abnormal turn rate as well for an ally if they lack it in their base kit too!
- Transformed BRV/HP command (40%). We've seen this one a few times too with Aerith, Sherlotta and Yuna: the upgraded BRV/HP base buttons.
- Any Melee BRV attack (5%). This includes off-turn attacks and Machina is a special snowflake and gets 25% bonuses when he does the melee attack so those counters and LD traps REALLY start to add up.
- His Force Time is great not only because he himself benefits greatly from the FR, he can work in both aggressive teams (with Cor, Yang, etc) but he can also work with off-turn melee attackers as well (Faris, Cor, Yang, Auron, Galuf, Gladio, Eight, etc). Some of those listed units cover or lock but that's ok as even if Machina doesn't counter for 25% and 1 HP attack, you're still gaining 5% and a ton of damage from the cover/lock units!