I'm not sure how to word it, but I feel like legend should be used when you're talking about the tale/story and kismet would fit more when describing the outcome of said legend.
I.e. "Have you heard about the legend of that sakura tree? They say if you confess underneath it during closing ceremony you'll be together forever, just like it's kismet!" Besides, 'hidden kismet' just feels awkward in my brain. I am glad to see I wasn't the only one who cringed whenever I read jinx in the previous chapters though.