First of all, Kiseki will be decorated accordingly to the date, as usual.
Then, the actual event will start on the 14th, and last all the way till Friday. During this event, characters' thoughts on romance, whether positive or negative, trigger a Murphy's Law effect. Every time your character has a conscious thought about how they would like things to go, Kiseki will intervene and cause things to go directly against your character's intentions!
Kiseki's interventions can range from small details which would be difficult to notice are done by magic, to other events coming into effect, to the journals recording at really bad times, to huge crazy occurrences!
( Cut for TL;DR explanations )
I think that's about it! As always, feel free to ask any questions!