His family name is interesting, it sounded like the Neptune siblings' names, Shirahoshi, Fukaboshi, Ryuboshi, and Manboshi. Except his name has an additional -fu at the end.
Initially people think his name is chinese derivative because Kirin is originated from China, also it makes sense if translated from Pinyin. With that in mind, people translate Rimoshifu as Sunset Teacher or much better one Dusk Master which I think it fits better with the One Piece theme. The name Dusk Master fits a villain name very well in contrast with protagonist mostly linked with Dawn, Luffy's G5 has a lot Dawn abilities (Dawn Rocket, Dawn Stamp, Dawn Cymbal, Dawn Balloon, Dawn Pistol). The Dusk in his name fits his ability well, dusk usually signify the time where people should start sleeping and dreaming.
Since he is now revealed very likely as half fishman and thinking back of the similarity with Neptune siblings' name, I think Rimoshifu is mistranslated. Let's see what the Neptune siblings' names mean.
Shirahoshi - White Star
Fukaboshi - Deep Star, Shark Star (he is a shark)
Ryuboshi - Dragon Star, Royal/King Star (he is an Oarfish)
Manboshi - Thousand Blessings, Sunfish Star(he is a Sunfish)
As you can see, their names have a Star at the end of their name. If Rimoshifu is changed to the Neptune Siblings' naming format, the translation should be Dusk Star Symbol. I'm not sure whether it's accurate or what Oda intended to be, but it fits well with Imu's ability. The Abyss Pentagram looks exactly like a star symbol.
The name Rimoshifu might also formed from the combination of the Neptune Siblings' names, (Ry) (Ma) (Shi) (Fu). Just to make him as a counterpart of the royal fishman family.