Sho, oddly enough, is of the Sun arcana while his alternate personality is of the Moon. Tsukuyomi is the god of the moon, born from Izanagi's eye after he cleaned himself of the filth of the underworld.
While the Sun arcana is one of happiness and optimism, Sun characters in Persona tend to be characters put into extremely depressing circumstances. They do, however, tend to end their social links on positive notes, representing their optimistic nature breaking through.
The Moon arcana consists of subconsciousness, creativity and madness. Minazuki is an alternate personality, so it's a fitting role. Not to mention his persona is Tsukuyomi.