Gods' side :
The god of war - Nataku . He is also known as the killer doll and thus , no one dared to be his friend . He hated his life and trust no one till he met Son Goku . He liked Goku and wanted to know his name and since Goku was the first person who showed him kindness , he wanted Goku to be in his side each time he was hurt in a battle . But , his father ordered him to stop meeting Goku . There is very less we know about Nataku since he always sat silently in heaven with Kanzeon .
Godness of mercy - Kanzeon Bosatsu . I know little about her as the anime did not really focus her background . You may see her always playing a kinda of chess which tells the fate of the 4 travellers . She is the person who ordered Kanzo to look after Goku and she seems to know almost everything !
Demon's side :
The son of Gyuuma Ou , Kougaji . He is a friend and a foe of the Sanzo's party . His aim is to get the Sultra from Sanzo while at the meantime , he respect the 4 of them . He trained himself well so as to defead Goku ..... but he is not a bad person entirely . He is very caring and loyal to his followers and will do anything to bring his mother back to life .
One of Kougaji's follower - Yaone . She is kind , polite and a sweet person . She is in love with Kougaji and will do anything to make him happy , ( I doubt that Kougaji is in love with her too ) since he was the one who rescued her from being killed . She is also attracted to Hakkai at the sametime ^^ .
One of Kougaji's follower - Dokugakuji . He is Gojo's older brother who saved Gojo when his mother tried to kill him . He is very loyal to Kougaji since Kougaji give him meanings to his life .
One of Kougaji's half-sister - Rinrin . She is the joy of Kougaji and seems to be a younger sister to Yaone . She is very attracted to Sanzo which made Sanzo and the others running away from her each time she tried to bring up a fight with them . Her attitude is sorta like Goku's , though she is a half-sis to Kougaji , he loved her deeply . She seems to be very stupid and childlish at time , that's why I like her ^^ .