Tarba is a scoundrel from a remote region. According to his information box, he and his gang rob people coming out from the Deeprealms, or more specifically, those coming from Shiro's Deeprealm.
In Shiro's Paralogue, he arrives at his father's world and finds it rather dull than what Ryoma told him. Almost immediately, Tarba spots him and demands Shiro to give up all his belongings, or he would kill him. Shiro refuses and decides to fight him and his gang. Fortunately for Shiro, Ryoma was notified of his disappearance and quickly found him fighting off Tarba's gang of ruffians. Tarba is either killed or captured depending on the player's decision.