The fourth descent, Narasiṃha the man-lion, is the tradition's great riddle-solution, a story about how love and faith find the crack in cruelty's armour. It opens with Hiraṇyakaśipu, an asura king who, through fierce austerities, wins from Brahmā a boon of near-perfect invulnerability: he can be slain by neither man nor beast, neither by day nor by night, neither inside nor outside, neither on earth nor in sky, by no weapon, by no created being. Believing himself beyond death, he forbids all worship but his own.

His own son betrays this tyranny — not by rebellion but by devotion. The boy Prahlāda is, from infancy, wholly absorbed in Viṣṇu. No threat moves him; in the Bhāgavata's telling he is cast from heights, trampled, burned, poisoned, and each time emerges unharmed, serene in his certainty that God is sarvatra — everywhere, in all things. His father, enraged, demands proof: if God is everywhere, is he in this pillar of the hall? Prahlāda answers yes. The king strikes it.

From the splitting pillar bursts Narasiṃha — half man, half lion, a form that belongs to neither category and therefore evades every clause of the boon. He seizes Hiraṇyakaśipu at twilight (neither day nor night), upon the threshold of the hall (neither inside nor outside), draws him onto his lap (neither earth nor sky), and rends him with his claws (no weapon). Every loophole the demon thought he had closed is reopened by the impossible logic of the avatāra. Invulnerability becomes the very shape of the trap.

What unsettles devotees and delights theologians is the avatāra's fury. Narasiṃha is the most terrible of Vishnu's forms, blazing with a wrath that even the gods struggle to calm. In many traditions it is the gentle Prahlāda himself — or, in some Śrī Vaiṣṇava and folk accounts, the goddess Lakṣmī — who finally soothes the man-lion, drawing the protector back from the protector's own rage. This pairing of terror and tenderness is the heart of his cult: Narasiṃha is fearsome to the cruel, but he is the boy's own dear Lord.

The story is beloved across regions, with distinctive local forms — the serene Yoga-Narasiṃha seated in meditation, the ferocious Ugra-Narasiṃha mid-strike, the tender Lakṣmī-Narasiṃha with the goddess on his knee. Through them all runs Prahlāda's quiet teaching: that no power, however armoured, can stand against a heart that refuses to fear, because the One it trusts is present even in the stone.