Ym is a Demon in the Megami Tensei franchise.
Yamm, also spelled Yam, is the personification and god of the sea in ancient Northwest Semitic polytheism. Famously in the Baal Cycle, he competes with Baal for title of king of the gods and is El's preferred choice, but he ultimately loses.
The localized name, Ym, represents the name without vowels as written in Ugaritic, which uses an abjad script, rather than the actual pronunciation.