personally i don't think riou would go to one himself, but he would support anyone who did go.

i have a couple of reasons.

1: he doesn't do well in crowds in canon. those parades are too loud and overstimulating if he's right in the middle of it so he would rather just keep to himself

2: i think riou is in the closet, at least to most people. it's not that he's ashamed of his identity or something like that, i just think he doesn't feel like it's anyone's business. he's out to very close comrades, but he just doesn't say anything. if he goes to a smaller event like that, he might just go in regular attire with none of the flags and stuff.

sorry if this isn't the response you wanted!!! forgive me lol