I generally try to write my thoughts and impressions in a collected manner, but surely I can gush a little bit at this point? I love how the story has come full circle, it feels like the author painstakingly planned every little detail from the beginning. Each aquarium club show throughout the series was a landmark to highlight the development of the main characters, first when Konatsu was just starting out and going through the ropes, then stepping up to do it on her own in Koyuki's absence, then together with Koyuki who got embarassed of showing how much she enjoyed herself, and finally now with Konatsu as club president and Koyuki joining in and displaying her fun to everyone.
Even bit characters like Koyuki's classmates went from being intimidated by her and putting her on a pedestal, to dragging her along with good intentions but without understanding her needs and worries, to finally seeing and accepting her for who she is. But the one who grew the most out of the side characters is probably Fuyuki, who was childishly annoyed at being considered a mama's boy by his friends last time they went together at the school festival, and who now willingly remained with her as they bond over something they both like.
I'd have too much to say about Koyuki and Konatsu themselves, but it's not really necessary as all the callbacks were pretty clear in the story itself. I just want to express how satisfying it is to see how it all came together with Koyuki's line. Konatsu hiding her face behind the menu while expectantly waiting to see if she'd figure it out was really cute. And for all her previous worries about not wanting to be selfish and not being able to tell Koyuki everything she wanted, it's just so fitting that in the end she conveyed all her feelings without having to say a single word, and for Koyuki to finally be observant about both her own feelings and Konatsu's. They've come so far.