Nushi is a colossal Akrid living inside E.D.N. III. Somehow Nushi is a means to produce pure Thermal Energy, by purifying the Thermal Energy that the planet produces. If Nushi comes under threat it can call on other Akrid to aid it, like white blood cells protecting a host. It also has the means to summon the storms seen through out the game as a defense against any attackers.
Jim Peyton and Caleb Isenberg has their final battle in the heart of Nushi. Jim Peyton came out on top by killing Isenberg who got roped into the drill along with Peyton. Jim lost his left leg but also ended up killing Nushi but refused to tell anyone about it and instead, like Souichi, decided to protect those who he endangered. Without Nushi to keep normalcy of the planets climate, both Gale and Mira created the Harmonizer that mimicked Nushi.