It's available in ep15:
Protector: Iolia Valley, after collecting all four Crustal Plugs go to the upper right cave, use the purple crystal to open the way to the upper exit, step outside and it's there (path towards the Sableye Cave)
Use this next time:
-I think you need to be in ep15 to catch him
-Same as the first, you need to be in ep15
EDIT: What I meant for ep15 is you need to be in the old city.
-Idk but is it really tanzan mountain?
You need to visit sunset circle, azurine lake, and rhodochrine, Im not sure which forest either in beryl or jasper. They'll give you hints where corin rogue is, go there and after that you visit the 3 spots again
Then rename the sprite to "boy_walk" and take note while your charcter is running surfing riding a bike, etc. the new sprite wont show because you just replace the walk sprite.