>>714846882You are not off, Shingon Buddhism is Tantric after all.
The mask is refered to as Kishin, which is like a Demon God, more usually translated as Wrathful Deity.
They are a class of Gods in esoteric Buddhism, usually depicted as smiters of evil demons who threaten Dharma.
The game is structured like the diamond mandala, with an emphasis on the four cardinal directions, and it is not a coincidence that the ones who you have to surrender the masks to are these demons representing those cardinal directions.
At the center lies the moon and clocktown. Who sits at the center of the Diamond Realm Mandala? Mahavairocana Buddha, the primordial cosmic Buddha, and so I would actually say that the Fierce Deity mask is a direct symbol of Fudo Myoo. Who is the Wisdom King, a Kishin, considered an emanation of Mahavairocana Buddha and seen to lay at the center of the mandala.
To further the Buddhist connection, where does the fight with Majora start? Under the Boddhi tree.