Reinhardt (WT)

AD solo and Rouse AD give Reinhardt an extra 12 def and atk if alone. Brazen AD kick in if his health goes below 80% thus giving an additional 7 atk def. To give an idea, altogether he'd be doubling or quadrupling with 65 atk and going into combat with 50 def. This let's him work pretty well as a hard hitting physical tank.

He'll further debuff the enemy with chill def, making it easier to take down very tanky enemies. Alternatively, you can keep vantage to preemptively assault any enemies, though it might be hard getting him into vantage range without putting him in danger against magical units/blue units.

Moonbow is a nice special due to the low cooldown though glimmer works too.

A Skill Alt: Distant Counter
B Skill Alt: Vantage
IV Alts: +Def, +Res, -HP
Seal Alt: Brash Assault

(Note: The following mostly applies to the original suggestion)

With guaranteed double attack on both phases, and a fairly solid defense stat of 31 (neutral), this set's primary focus is enemy phase, though you can still utilize this on player phase if you get lucky with positioning or don't mind using another unit's turn to activate his Bond Skills, though you will still be lacking the ability to quad them, but if you can't kill them with a player phase 56-59 Atk double, you likely will only be charging their Ignis or Aether up to be used on you in their followup attack, whereas you can get away with anything more than 3 cooldown if they attack you first, and can still quad them after their followup without the penalty of facing a charged special afterwards (unless they are also running a quad build AND have enough bulk to live through your (56-59 + buffs) Atk quad).
Sol provides self sustain, and is likely to go off either every time you retaliate, or at the beginning of your third attack (if not the latter, add +1 to all the specials they can activate when you're in enemy phase).
C skill is team dependent.

+10
Res Blessing
-----------------

Meisterschwert is a dual-phase 11Mt Brave Sword, which really speaks for itself, and along with his balanced stat line, dictates what kind of role Reinhardt wants to play.

Luna remains the most consistent special for a Brave weapon. Blue Flame, in my opinion, does not work as well on cavs due to their movement restrictions.

Distant Counter is a no-brainer as it allows his weapon to shine on both phases. Reinhardt can take on some ranged threats, especially since he is paired with my +10 Gunnthra, who provides him a boost to Res and HP through her Blessing, meaning once buffed, his defensive stats are quite solid.

Vantage is there as a filler, really. He comes with it by default, and it works well enough for the time being. Due to IS' hateboner for cavaliers, he is locked out of most new B skills. QR allows him to quad in enemy phase, but requires Aether to sustain, which is a drop in his damage output. In PvE, the Fury/Desperation/Brash Assault meme combo works well on him, but it's somewhat janky and not my first choice.

Reinhardt (WT) is an incredibly strong unit when working with a primarily enemy-phase build that also works for player phase. It's especially good as a build for RD and GC. Essentially, the idea is to attack enemies until you get under 75% Hp. You don't have to worry about being KOed that much thanks to Rein's overall solid bulk. That's when the fun starts. Using Vantage (and boosted by Brazen Atk/Res 3), he'll instantly KO enemies who try to initiate on him. This spreads the Def Smoke effect, which in turn makes it easier for him to KO any other units who'd initiate on him. Moonbow is nice for this build so he can have consistent activation, and it helps him break through tanks who might be initiating. Brazen Atk/Res is especially nice because it boosts up his Res even further, making low-hp WT Rein still extraordinarily hard to break.

This man is an unparalleled powerhouse.

Atk: 49+6(Death blow)+6(Odd Atk Wave)=61
Special can either be moonbow or glimmer, but when initiating combat, it is safer for Reinhardt's hp to below 50% at the start, with both desperation and brash assault activated. Quad attack without giving an opponent to counter & moonbow/glimmer is powerful enough to defeat almost any hero within feh. This condition can be resolved through the use of Reciprocal Aid. However, this build is frighteningly vulnerable against enemy phase, and takes couple of units to activate reinhardt's passives. It is risky, but somewhat worthwhile.