Fusing Personas in Persona 3 Reload is the best way to create a powerful roster to aid you in battle, and Helel is a Persona worth fusing as early as possible. Unfortunately, Helel requires players to reach a fairly high level before they have the option to fuse it, so it will be available late in the game unless players grind up their level in Tartarus.
https://screenrant.com/persona-3-reload-how-to-fuse-helel-combinations/