These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Kyoukai no Kanata
Ass Pull: Some people accuse Mirai's resurrection at the end of the series to be this, as it happens suddenly and with very little explanation.
Base Breaker: Mirai is considered a bad heroine by many. Her inconsistent attitude and her klutziness being out of place are cited as the main factors.
On the other hand, others find her portrayal a refreshing protagonist who doesn't fall into one of the many expies common to anime.
Opinion on the ending is divided, since many fans are either pleased that the series ended on a happy note, or angry since they percieve Mirai's last minute resurrection as an Ass Pull.
Covert Pervert: The fact that Ayaka has a personal collection of nude photos of Ai (in Youmu form and otherwise) raises some eyebrows.
Not to mention the fact that Akihito apparently pays good money for pictures of bespectacled hotties in Fanservice-y costumes. Though there's really not a whole lot of "covert" from Akihito, what with how he proudly proclaims his glasses fetish to the world. He even calls himself a pervert at some points.
Mitsuki knows where to find a lot of BL Audiobooks to prank her brother with.
Dude, Not Funny!: The scene when Akihito and Hiromi objectify Mirai right in front of her.
Mirai having to do rather risque photoshoots to make ends meet counts too.
Ho Yay: Hiromi's habit of teasing Akihito can be interpreted as this. Though one has to admit that he is a little too touchy-feely with "Akkey" for it to be merely normal teasing.
Episode 7 takes this to a new high when Mirai (while freaking out) speculates who Akihito has in his apartment with him. He vehemently denies any name she says but when Hiroomi's rolls around he doesn't say anything. At all.
It may be that he was just tired of her wildly flung accusations, since she had been running through the names of every person they knew before saying Hiroomi's name.
Akihito jokes Hiroomi is falling in love with him, when he worries about how the Calm will affect Akkey in episode 8.
In episode 9 Hiroomi seems to be the only one who actually puts an effort into saving Akihito from being killed by Mirai. He goes as far as to yell at Izumi while he is usually very quiet around her.