Shoko has fallen for Ishida. She gives him a gift and tells him she loves him. Out loud. This is no good, because her pronunciation is off enough that Ishida thinks she said "The Moon" and doesn't understand.
(Moon/Love puns are traditional in Japanese for some reason.)
Ishida asks Yuzuru if Shoko is avoiding him. She suggests he ask her out; if she doesn't want to, she'll just say no.
Ishida invites her on a group trip to an amusement park. But someone didn't vet the guest list, because Ueno is there.