Sakya is short for "Sakyamuni", otherwise known as Gautama Buddha, the founder of Buddhism.
After Buddhism started to become prominent, Hinduism began to regard him as an avatar of Vishnu. Sakya's mother is Queen Maya of Sakya, the name is originated from the Hindu concept of illusion, Maya.
Sakya appears as a randomly appearing boss in the second door of the Abandoned Factory. Defeating him causes him to drop his Material Card, Buddha's Words, allowing him to be fused in the Velvet Room.
Persona 2: Eternal Punishment
Sakya appears in the last part of Tatsuya's Scenario and resides at the Tower of Perseverance inside Kadath Mandala. Asking the party what the self means to people and to Maya who shares his mother's name. He speaks humbly to the party and gives them the Trapezohedron of Perseverance after asking them to spread the enlightening teachings of Buddhism.
In the main scenario, his Material Card can be obtained by defeating him in Room 2 of the Bomb Shelter.
Fully recovers HP (or removes ailment in addition).
Gallery
Sakya's Material Card, Buddha's Words
Trivia
The name of Sakya's Material Card in the Japanese and Eternal Punishment English versions, "Yuiga Dokuson" (唯我独尊) is part of the first phrase he ever spoke when he just had been born. The whole phrase is "天上天下 唯我為尊 三界皆苦 吾當安之" which can be loosely translated as "above the heaven and below the heaven, I am the only one of utmost dignity. Adversity plagues the Trailokya (three realms), I shall be their savior."