Jozu on 30 April 2013
Yeah they sort of got replaced by the newest adversary turned ally. Tien was Goku's rival but was replaced by Piccolo Jr who in turn was replaced by Vegeta.
The characters got that strong that the lesser characters weren't able to keep up at all and just became useless and they were written out of it a little.
Krillin still had a good role though until the Buu arc.
With this new movie Goku has now got a new rival in Bills and is two transformations infront of Vegeta who could be the next to become useless.
