Complex sentence: Mokkun is actually, see Teng (mythology), who prefers to be called Guren is one of the twelve "shikigami" called the, who has pledge his loyalty to Seimei and help Masahiro to surpass his grandfather.
Split into simpler sentences: Mokkun is actually, see Teng (mythology), who prefers to be called Guren. He is one of the twelve "shikigami" called the, who has pledged his loyalty to Seimei and is helping Masahiro to surpass his grandfather.