Younger twin in the Apapocúva-Guaraní cosmogonic cycle. Conceived by Ñanderu Mbaekuá ("Our Father Who Knows" — a separate divine figure from Ñamandu, his half-brother Kuarahy's father) of Ñandesy. The dual-paternity-of-the-twins structure (Kuarahy by Ñamandu, Jasy by Ñanderu Mbaekuá) is canonical to the Apapocúva cycle and structurally distinguishing — the half-brother relationship is the framework that allows the twin-figures to embody complementary cosmological domains (sun-and-moon, day-and-night). Survived in Ñandesy's womb after her death at the dwelling of the Yñvaguasu monster-jaguars; raised among the jaguars by their grandmother. On growing to youth, learned with Kuarahy the truth of their mother's death; together slew the monster-jaguars by luring them across a river that collapsed beneath them. During Kuarahy's attempt to resurrect Ñandesy by gathering her bones and singing the resurrection-song, Jasy looked prematurely (or laughed, in some recensions) — preventing full resurrection; the error of the younger brother is the structural pivot that determines the partial-resurrection outcome (Ñandesy becoming a tapir or the Pleiades constellation rather than fully restored). Ascended to the celestial vault and became the Moon. In the Apapocúva tradition, lunar eclipses are interpreted as the jaguars pursuing Jasy across the night sky — the continuing-presence reminder of the foundational mother-vengeance cycle. The eclipse-as-jaguar-pursuit cosmology preserves the foundational narrative in the present-day calendrical-and-religious practice of Mbya-Guaraní and other continuing Guaraní subgroups.