Mantis's Links
When Rooster decided to leave the clan for good Mantis was ordered by their master (a father figure) to "erase" Rooster. That fight was what made Mantis realize how fun and equal of an opponent Rooster is, and he wouldn't stop bothering Rooster from then onwards.
Rooster and Mantis used to be from the same clan and studied under the same master, Rooster's father. Rooster wants to put the rough lifestyle behind him and lives a normal life now, but Mantis wouldn't stop bothering him for a fight. He holds no hatred for Mantis, just pure annoyance.