Rikyako’s addiction to sour things is well-documented. She talked about her intense love of vinegar and her addiction to umeboshi (pickled plums that are known for being very sour and salty) back in 2016 when she was interviewed on “KaneTomo Seiyuu Laboratory”:
Kaneda: I don’t understand why you like pouring vinegar on everything.
Rikyako: (genuinely shocked) HUH? You don’t?!
Rikyako: I love that feeling when your throat dries up from the sourness~ ♥
Kaneda: *judging her*
*GLUG GLUG GLUGGGG*
Demonstrating the ungodly amount of vinegar she pours on her food.
A container of vinegar this big wouldn’t last her a month.
Rikyako’s love of sour food has even been brought up by her fellow Aqours members on UraRaji. (Subbed segment of the relevant UraRaji episode [here])
During UraRaji Ep15, Arisha and Ainya mentioned Rikyako's ridiculous plum intake, saying that Rikyako could probably be lured away by umeboshi in the same way that Ruby was baited with candy by Chika in the anime. Apparently, before one of their live performances, Rikyako absolutely destroyed a pack of umeboshi in no time while waiting backstage. Arisha was very concerned for Rikyako's health since umeboshi has a high salt content.
It turns out that this habit of Rikyako’s was evident as far back as her middle school days. Back in 2005~2006, Rikyako was part of a young idol group called “Jewel☆Hands” that released a DVD of their activities. In one part of the DVD, a cameraman goes around to each girl and asks them what their impressions are of the other members. One member in particular had something interesting to say about Rikyako:
Q: What about Rikako?
A: Rikako is...how should I put it...
A: A lemon.
The cameraman is understandably confused, so the girl explains why she associates Rikyako with sour food:
