Yes, Thrianta are rare, but I haven't seen any bunnies with that vibrant a red/orange color before other than Thriantas. It may be a color for nethies, and I to think he looks like the older one. Thrianta are rare but it's possible they're one of those breeds that has gained a hold in Japan because they're so beautiful, and a good size for pets.
I wonder though if the colour is somewhat altered by the camera's red filter. It looks somewhat different in the picture where all four are together.
If there were more in the shop why not go back with a Japanese speaker and ask.
It's an adorable bunny whatever the breed is.
He looks so much like my Poppy!!! His colouring is almost the same, how it fades a bit around his middle section and gets lighter towards his underside!!! They could be brothers - LOL! Will try and post a good recent pic of Poppy for you.... I don't know what he is either.