I'm not sure what you would consider a "reikao story"... but maybe Rockin' Star? iirc it was loved by a lot of reikao shippers at the time it came out, but that may just be because we didn't have many, or maybe even any, stories where they had a one-on-one conversation before that lol. And it also was one of the first times they acted like "parents"/older siblings towards Koga and Adonis in a story other than Repayment Festival. It's very hard to find full translations anywhere, if there are any out there at all though