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By Imperial Year 1185, Indech had taken on the form of a magic beast. He became The Immovable, the guardian of the ancient temple at Lake Teutates. Linhardt told Leonie that a holy weapon that did not require a Crest to wield was hidden at Lake Teutates, leading to them and their allies traveling to the area to retrieve it. They confronted The Immovable in combat, who agreed to give them the weapon they sought upon his defeat. The weapon turned out to be none other than the bow of Saint Indech, The Inexhaustible.
If Flayn engages The Immovable in combat, he expresses joy at getting to meet her and nearly calls her by her true name, Cethleann, but she shushes him, referring to him as "uncle". If Linhardt engages The Immovable in combat, he deduces The Immovable's true form, but is urged by The Immovable to play ignorant. If Byleth engages The Immovable in combat, he realises that they are the incarnation of Sothis, and resolves to test their strength.
His name is a reference to Indech, King of the Fomorians in Irish mythology. In some versions of the story, Indech is killed by the Morrigan during the Second Battle of Maige Tuired.