She had some real courage as a 5 year old, didn't she? You go, Chitoge! Reclaim that love!
I know this doesn't mean she actually did manage to make the promise, but still. That conviction she had at that age is really inspiring.
Also, it was adorable seeing them all as little kids, all together. And, of course, Haru was there, too. Why wouldn't she have been? If Kosaki was, and I think her mother Nanako, why would Haru have been left at home?
Also, hahaha... Marika's reaction was priceless. Always butted heads with Chitoge, I suppose, ever since then.
Yui's reaction is more just pure surprise, with so much innocence. Kosaki's basically going 'wait, what?!' ...