Brave Dimitri

Weapon: Moon Gradivus (+Eff)

Assist: Movement Assist

Special: Noontime / Moonbow

Passive A: Atk/Def Unity / Steady Posture / Bracing Stance

Passive B: Blue Lion Rule

Passive C: Atk/Def Menace / Spd/Def Menace / Atk Smoke 4

Seal: Spd/Def Solo / Def/Res Solo / Atk/Def Form

• There is very little to improve upon in Dimitri's base kit, as almost all of his heavy lifting is done via his Moon Gradivus and Blue Lion Rule, which together enables Dimitri to counter from any range, reduce his damage taken by a percentage and a flat amount, accelerate his Special, and enable him to counterattack twice. What more could you ask for?
• Still, there are a few tweaks to be made. Due to Unity skills pushing debuffs out of the meta, Dimitri may not be debuffed at all, in which case he benefits more from a Guard-inflicting A slot, such as Steady Posture or Bracing Stance. Defense is absolutely his most important stat to buff, after which he has to choose between Attack (for faster kills), Speed (for dodging doubles), or Resistance (for surviving mages). The kinds of matchups he's in dictates what his secondary stat should be present in his A slot, but all of them function similarly.
• For his C slot, Atk/Def Menace will be far more useful on him as a way to buff himself and debuff his foe. Alternatively, you could use Spd/Def Menace to try and increase his Speed differential to avoid doubles
• You could also go with Atk Smoke, which buffs Dimitri throughout his next Player Phase turn, allowing him to freely attack into Speed-focused units.
• For his Special, Dimitri can take his native Noontime for healing - which can be vital if he's being doubled by his opponent - or swap it out for Moonbow for extra damage.
• His Seal slot is all about further stacking stats - either via Spd/Def Solo or Def/Res Solo, both of which grant him additional Defense. Alternatively, he can take Atk/Def Form to raise his stats even more and remove the Solo requirement (making it easier for him to work with his prf and Unity's prerequisites), but doing so leaves his Speed in a somewhat lackluster place.

Weapon: Moon Gradivus (+Eff)

Assist: Positional Assist

Special: Noontime / Moonbow

Passive A: Bracing Stance / Atk/Def Unity / Def/Res Ideal

Passive B: Blue Lion Rule / Atk/Def Bulwark

Passive C: Atk Smoke / Def Smoke / Pulse Smoke

Seal Slot: Def/Res Solo / Distant Def / Bonus Doubler

• This build gives up on building Dimitri's Speed in favor of patching up his shoddier Resistance while keeping his Defense high. This allows Dimitri to more effectively wall nuke Speed-invest mages like Brave Lysithea, who would have outsped a Speed-invest Dimitri anyway.
• Without a Far Save support, Dimitri has to worry more about being attacked consecutively, therefore a Smoke skill wouldn't go awry - Atk Smoke, Def Smoke, or Pulse Smoke are all useful in different ways, with Atk Smoke lowering his incoming damage, Def Smoke increasing the Def differential for Blue Lion Rule, and Pulse Smoke for disabling ready-to-go Specials.
• As an omnitank, Dimitri also appreciates additional support, particularly stat support in the form of units like Kaden or Askr. Since he wants to buff his Defense as high as possible to give him a flat damage reduction, stat boosts and bonus doublers are very useful - just be sure that Dimitri isn't facing down any debuffs or Panic, or continue using Unity on him.
• If using him in a game mode like Summoner Duels, consider running Canto Control on him, as his C slot is rather flexible and a well-invested Dimitri can tank without it while also ruining your opponent's mobility.

• Fun Fact: A Kaden with +6 Def buff, on a +6 Defense buff with Bonus Doubler Seal Dimitri with Def Boon, Atk/Def Unity, Dragonflowers, and merges... reaches 81 Defense, which is 16 flat damage reduced with every hit - not including his additional 40% Damage reduction from BLR
• Even more Fun Facts: Add Ashera into the mix in Astra season for Panic negation (if not using Unity), or Askr in Light season for +4 to all stats and Time's Pulse, potentially allowing Dimitri to run more powerful Specials.