they are different souls inside his body, Both of them are different existences (i belive it was mentioned both of them were ancestor and descendant). they will interact a lot with Badul Specialy Sanai who is a battle maniac, the older Badul Gets the less they appers until one point Masaharu Stop talking to Badul because he realize it's badul's life not his. Sanai in the other hand when badul is facing a Battle it was impossible to win Sanai says to him that he must die in battle with honor and decide to sent Selina and Seilurn to safety while he fight, both of them refuse and beg badul to live, Sanai get annoyed and is about to hit them badul notice it and tried to stop it but it was Masaharu who did it he is the voice of reason to stop sanai telling him that both of them are nothing but observers and it's Badul's life , Sanai realize that he can't fulfil his wish of dying in battle and Goes to Sleep.
After that Sanai Only appers to give advice to badul when he is truely Clueless of what to do or when a Strong Enemy is Nearby for him to have a "Friendly" Match (badul fights on his on after Sanai when to sleep) and Masaharu never appers again because he already give Badul all his knowledge