Shurimon is the creator of the DigiMemories & an ally of the DigiDestined.
When SkullSatamon destroys the Thunder Digimon & damages the first set of DigiMemories permanently, the DigiDestined seek out Shurimon for assistance. At first, Shurimon isn't easily convinced that the DigiDestined seek out the DigiNinja Power for the right reasons, but after hearing them out, he soon changes his mind. Shurimon bestows on them new DigiMemories & they receive Ninja Digimon, & from then on assists the DigiDestined in battle whenever they need him, such as providing Cody with back-up when the other DigiDestined are turned into soccerballs by Footmon.
He is captured by Lilithmon & Tactimon to power the Shogun Digimon. At the same time, a mind-controlled Mia steals Maggie's Cranemon DigiMemory & seizes Aquilamon, putting the Ninja Digimon out of commission & leaving the DigiDestined vulnerable. They eventually get control of the Shogun Digimon & reclaim Aquilamon, & Shurimon escapes shortly after. He is recaptured by Barbamon & linked to Raremon, which causes all damage to Raremon to transfer to Shurimon, but he soon escapes again & helps the DigiDestined defeat Barbamon. He continues to assist the DigiDestined after this.
As a ninja master, Shurimon has a wide array of powers at his command. He has a large white cloud that he rides into battle on, & can disappear into puffs of smoke at will. Shurimon & his Temple of Power are both key elements to the DigiDestined maintaining their DigiNinja Powers.
Shurimon resides inside a vase within the Temple of Power, which is itself located in the Desert of Despair. He is also the creator of the original DigiMemories, the Digimon Bio-Hybrids, & presumably the Shogun Digimon & the Aqua Warriors' DigiMemories. After the DigiDestined gain the Zeo Digimon, Shurimon isn't seen again, & Alex comments that he is once again residing at the Temple of Power.
Musyamon is the battle mode of Shurimon that he uses to transform to the size of NinjaOmnimon. Normally, Shurimon wields shurikens in battle, but as Musyamon, he is armed with a large & powerful katana. He is also able to generate & throw explosive fireballs from his hands, which are often instrumental in destroying Lilithmon & Tactimon's Digimon. In order to transform into Battle Mode, Shurimon will usually call out "DigiNinja Power, Now!" or the traditional "Shurimon, digivolve to...!" & then digivolve. Typically they are just a distraction, so the DigiDestined can go in for the kill, but his fireball that hits at the same time as ShogunOmnimon's sabre actually is what finishes off Raremon, once all his energy is depleted.