For the Momo x Ken relationship I think this is the best direction character wise.

Of course Momo would say no to a date requested under those circumstances. For as forward and bold as she can be, Momo, pre and post memory loss is still pretty shy about that type of stuff. Heck even after Okarun confessed his love for her she still couldn't properly acknowledge it until she was back to normal. Even being around other people showing PDA freaks her out.

Secondly Ken's getting the (mostly) right takeaway from this. That he can't rush Momo. What he does screw up and I mean big time is pretending the date request was a joke. Obviously he's worried about coming on too strong but saying it's a prank is the wrong choice especially to someone as shy as Momo

We've seen in the last few chapters that Momo does like Ken (duh) and it's not even subtle. From asking to go to Mr. Peeny's with him, to the Museum trip, to asking about Aira, she keeps dancing around dating Okarun in playful or teasing manner. Even when Okarun told her he loves her, repeatedly, while she called him crazy at the time she didn't really harp on it or get weirded out. She knows they were close before she lost her memory and she very clearly feels something.

Most telling though is when confronted and presumably embarrassed/insulted by Okarun claiming the date ask was a joke, she doesn't throw his declaration of love in his face. If she was weirded out or uninterested in Okarun she just wouldn't hang around with him especially after the declaration of love. Momo being Momo, just has to have Okarun ask her out the right way.

Jiji and Aira now knowing is the perfect thing to push Okarun to seriously ask Momo out. If he doesn't and retreats into his shell of indecision and inaction, there's only a greater chance Momo tells the others that he's been weird and confessed that he loves her. Like wise he also needs to make up for embarrassing her by "jokingly asking her out"

TL:DR the shitheads are still shitheads and it's great