the caliber expected of a grand champion
Sumo term referring to the mental fortitude, dignity, and character befitting a yokozuna. Often used metaphorically outside sumo to describe someone with outstanding presence or leadership qualities.
He is still young, but he is a player who gives off the aura of a grand champion.
真のリーダーには横綱の器が求められる。
A true leader is expected to have the caliber of a grand champion.
Compound of 横綱 (yokozuna, 'grand champion') + の (possessive particle) + 器 (utsuwa, 'vessel' or 'caliber'). The expression draws on the sumo tradition where a yokozuna must embody not only strength but also dignity and moral character.