Sankaku Mado no Sotogawa wa Yoru

-Focus on story of people with supernatural/abnormal powers. In Pet it's entering minds/memories of others, in Sankaku ghosts, curses and such -main duo with a certain dynamic (balancing near that BL line) -characters interesting from a psychological angle 

both animes contain love between boys  

- Both have BL themes, being adapted from a BL source material - Both are Urban Fantasy, fantasy setting in a modern world. 

Bible to Gege for jjk, very similar as stated in the jjk fanbook, one of his favorite manga's and big inspiration - this is where Gege got his curses inspiration from - Similar character design  

Both deal with people having supernatural abilities of sensing Ghosts and forming a team later on. Though Ghost Hunt is more case oriented while Sankaku Mado no Sotogawa wa Yoru deals the personal lives of the characters. Both are very interesting and have the characters becoming a team to solve something together. 

Shiki has the ability to see spirits, so does Kouske (dead people) and they're both used in as detective fashion to figure out mysterious occurrences. I feel Kara no Kyoukai is a little more action packed, but more or less they're very similar 

Both revolve around the occult and taking care of incidents incurred by it. They also have a guy taking care and making use of the protagonists' special abilities.  

Similar dynamic and ending with similar looking characters.