Talk:Kara no Kyoukai Collaboration Event/@comment-64.251.56.100-20180209172320/@comment-96.4.9.130-20180209190150

They unlock another area, the roof, as well as it's quest Clear Boundary. You shouldn't be able to get there just yet, as the area unlocks closer to the end of the event, but when it does release you'll get the 99th quest "Complete Clear Boundary", and the rooftop will become available. So yea, that's what the keys do. Unlock the roof and the last mission/battle.