"ʻO kona kula ka hoa paio."

Translation: Her school is the opponent.

[RonRGB]

(link) https://manomano.io/definition/6221)

hoa paio

[PE] 1 Opponent, antagonist, adversary, enemy, rival.

[MK] 1 n Opponent, as in a sporting event. ʻO Punahou ka hoa paio o Kamehameha i kēia hoʻokūkū nei. Punahou is the opponent of Kamehameha in this game.

[LA] 1 n Hoa, companion, and paio, to contend.

An antagonist; a fellow wrestler or fellow fighter.

[scarvbarv]

Why 'O instead of He?

Is it because of the possessive?