Big Hero 6 Dark path

This is a tale of Hiro Hamada who goes down a very dangerous and dark path after his brother disappear which made people believe he was dead and after that Hiro snapped but those years of disbelief he finally convinced himself of his brother's death and that leads the Whole Big Hero six team to go under after Yama and his goons and fakes come in Hiro's life along with his thugs who were forced into working for him. Of course Hiro has his girlfriend who has powers and abilities of controlling elements of nature but with this San Fransokyo is grave danger and Hiro is sad still after four years with his brother being dead..or is he really?