Here are my thoughts and notes for the chapter overall, since you feel you "failed" Rikku this chapter:

Personally, I think it would have helped if the audience was somehow aware of Rikku's tendency to make "bad calls" prior or during the chapter, such as prior to the fight you would have a character from Rion's group mention that they hope he takes subduing Usaro seriously. Otherwise, I and probably anyone else would not have known that flaw in his character since it was never mentioned anywhere.

What also set up my expectation of Rikku was the chapter cover. To me, it showed that the conflict between him and Usaro would be taken seriously due to how dramatic the cover looked, and that the fight between the two would really show the stakes that he's in because of his allies being taken down earlier in the chapter.

One thing I want to note is that Rion's lightning attack was amazing because it can show how deadly he can choose to be, but it seemed like a Diabolus ex Machina due to how there was no indication that Rion would be involved at all in the chapter; since his involvement seemed to be very important into how this chapter would play out yet, I think it would have helped if he was at least shown in the chapter cover so the audience could expect him eventually. Otherwise, to me it seemed like him and his lightning attack was a contrived way to get rid of Usaro from the story for the time being since it happened within the last 3 pages of the entire chapter.

Overall, my expectations as a reader weren't met and I did feel frustrated with that, but I think it's good that you acknowledged how you personally felt with it as well because it can be a moment to learn, as a storyteller, a better way to portray your intentions and as a reader, I am anxious to see how the story will go from here.

I didn't realize that about Rion. My intention was to pull of a bunch of interesting surprises throughout the chapter, but I definitely didn't set up things properly.

I really hope Ursaro is okay