Sumo Wrestler (5e Fighter Champion variant)
by Marc SaindonWhile I'm tempted to make the Sumo wrestler a Monk subtype, the reality is that Monks are Dex builds and the Sumo would focus more Strength (to carry all that weight around) and Constitution. Sumo Wrestlers would not be developping mystical powers like Monks, although they can certainly multiclass into that career path as well.
Sumo in Mystara is the fighting style popularized by Tortle-folk of Yasuko, which I call Kappa (use whatever you want). The (made-up) tradition was for two rival Kappas to see who could topple the other on his shell, leaving that opponent vulnerable and thus defeated. Sumo gained popularity in the wharfs among the lower castes, and gradually garnered enough acceptance that other races of Yasuko - even Rakasta fat cats from the higher castes - started training their own champions. The sport has become popularized enough that Ierendi has been asking for athletes in demonstration competitions.
Nobles that are wealthy enough sponsor a Name-level Champion (all that eating is expensive), and wealthier Daimyos might sponsor a stable of them (that's you, PC) living under the senior wrestler's shadow and training until their own glory days. Wrestling victory brings prestige to sponsors, and there's quite a bit of gambling involved. Kappa Tortles still dominate events.
Champion as a Sumo Wrestler is built around various unarmed combat Feats (Tortle's Natural Armor helps) as Grappler, Athlete, Crusher, Tavern Brawler. Cross-training with Monk might help, although would probably be limited to the Way of the Open Hand. As public figures, Charisma, and Charisma-based Feats might also help the Sumo Wrestler win the crowds. Because of their strict dedicated training, they tend towards Law more than Chaos.
Notes:
Sumo
Fighter: Champion
Monk: Way of the Open Hand
(Image from: https://www.deviantart.com/artstylealice/art/Japanese-Sumo-Wrestler-1008942729)