Unarmed strikes are not weapons
The Combat section of the Player's Handbook explains unarmed strikes:
Instead of using a weapon to make a melee weapon Attack, you can use an Unarmed Strike: a punch, kick, head--butt, or similar forceful blow (none of which count as weapons). On a hit, an Unarmed Strike deals bludgeoning damage equal to 1 + your Strength ...
You cannot wield an unarmed strike, so this does not work
The Brace Maneuver states:
When a creature you can see moves into the reach you have with the melee weapon you're wielding, you can use your reaction to expend one superiority die and make one attack against the creature, using that weapon [...]
You cannot wield an unarmed strike. I come to this ...
Aasimar/Goblin Wild Magic Barbarian 5/Hexblade Warlock 12/Devotion Paladin 3 +76 on first hit, 56 on the rest
Feats taken: Great Weapon Master (+10), Sharpshooter (conditional +10), Charger (+5)
Items: Belt of Storm Giant Strength (+9) , Ioun Stone of Mastery (+1 to proficiency), +3 two-handed weapon of any description
Abilities from classes: