He is an anime-original character who appears in episode 34.
Shouta's dream was to become an artist. It's from this wish that his Guardian Character, Kuuta, was born. Tragedies occured in his family life, however, and made him doubt his dreams. He never saw Kuuta and doubted himself more as he moved away with his family.
He later comes back to his old house half a year later with an old paint set. The set belonged to his grandfather before he passed away. While talking to Rima Mashiro as the other Guardians were investigating, he fell into depression, turning his character to an X-Character.
Kuuta is later purified by Amulet Spade, and Rima encourages him to pursue his dream again.