BUR #26716 has been approved by @nonamethanks.
create alias rainy_(rbb) -> ketsuko_(rbb)
create alias blue_(rbb) -> hamko_(rbb)
create alias bell_(rbb) -> bellko_(rbb)
It seems like these original names were made up. The RainyBlueBell moniker is a combination of elements from the members' names, not a combination of the names of the characters. Rather, their names are Ketsuko, Hamko, and Bellko respectively (readings taken from their Niconicopedia page). Their BOOTH page also uses these names for their merch. I chose an alias with the age of the tags in mind, but a rename may be better when these names have never actually been used in any official sense (as far as I can tell, I haven't found any other sources that use them).