I've encountered that problem many times with new fish. Being in an unfamiliar tank with new fish, goldfish can get a little "skittish" and act completely terrified when you come in the room/walk by the tank. This behavior is very normal and will take some time to go away. I had a fish who hid in the plants for a whole week and only came out occasionally to nab some food! When I cleaned the tank that week and removed his precious plants, he was forced to mingle with my other fish and forgot all about his fears.
Expect your ryukin to act like this for anywhere from a few days to a couple of weeks - it's different for every fish. But sooner or later he/she will learn to associate you with food and not as a threat. When this happends, the fish will run (sorry, I mean swim speedily
) to the corner, bounce around like crazy, and even take food from your hand the way mine do.
Sometimes fish will act insecure if there aren't enough decorations/hiding spaces/live plants in the tank to make them feel sheltered. This can cause them to exhibit signs of fear. In the wild fish need places to hide and feel safe, and when they don't have that in a tank they can act very frightened. If your tank has ample 'junk' then there is nothing you can do but wait until he comes around - which he eventualy will.
Good luck and hope this helps!