Norn appears as the final boss of any Shinagawa Ice Cave instance except those created during the new moon period. By defeating her, there is a small chance to obtain Destiny's Chronometer, which will allow the player to fuse her. As in most games, she can be obtained through a fusion of Atropos, Lachesis, and Clotho.
"Goddesses of fate in Norse lore. They live below the roots of Yggdrasil and weave the threads of fate, which bind even the gods."
—Shin Megami Tensei: Strange Journey Compendium
As usual, Norn can be summoned by special fusion between the Moirae Sisters: Clotho, Lachesis, and Atropos. In the plot, she is however a fusion between three Disir sisters.
Norn is met as part of the EX Mission, Fateful aid, in the top floor of Sector Eridanus if the earlier EX Mission The madness of Yggdrasil has been completed. She is located in a patch of land recorded in the auto map data which is a logical impossibility considering Eridanus had been until then inaccessible. Upon entering then attempting to leave the room, Norn shows reveals herself to the protagonist and explains the situation; her form before the fusion into Norn was, in fact, the three Disir sisters who the protagonist had met in Sector Bootes.
She explained that she had been the unknown force intervening in his fight against Yggdrasil and cancelled the time-based powers he had previously stolen, allowing a second assailant to take down the rampaging tree after the protagonist was previously at the mercy of Yggdrasil. Norn reveals then the second attacker was in fact, the protagonist himself, seasoned and grown from his experiences so he could challenge Yggdrasil on more even terms. Norn then takes the protagonist to the past at Sector Eridanus for a rematch against Yggdrasil to save himself. With Norn supporting the timeline from the future, the violent tree was defeated, completing the ontological paradox, returning her time powers to her earlier selves and sealing Yggdrasil in a cycle of power and defeat he could never escape.
Defeating Yggdrasil unlocks him and Norn for fusion, and grants the protagonist the Nornir Ring.
Norn returns as the Ultimate Persona of the Fortune Arcana in Persona 4. They are available to be summoned once the protagonist reaches Lv. 72 or above and completes the Fortune Arcana Social Link (Naoto Shirogane's). Similar to its predecessor, Norn's fusion prerequisite in Persona 4 still requires the special fusion of Clotho, Lachesis and Atropos in the Velvet Room. However, Norn no longer learns the skill Panta Rhei, as Odin now learns the skill; to make up for this, Norn holds the distinction of being one of the two Personas (the other being Trumpeter) in the entire game that naturally learns the skill Debilitate.
"An immortal demon that physically exists in the past, present, and future."
After recruiting the ThreeTimeMaidens and beating the game, go back to the temples where Lucifer talks with Darklord/Lord Light. The three will fuse together to become Norn in the same room the discussion happened. It is also possible to earn a Norn by doing the Battlenet Tournament, which requires one battle against 100 opponents in a row.
Norn can do the dark type combo attack Doombringer with Ankuu, which does no defense damage for 25 MP.
Even though Norn are a group of Norse Goddess, they are usually made by fusing the Moirae Sisters which, while both have similar roles, the Moirae are from a different Mythology (Greek); the only games that averts this are the Demikids games.