Hatenkou Yuugi, Kuroshitsuji Recommendations
The art quality and the air of mystery are very similar in both. Both have humor and a dark past.
Both have a strong young protagonist that is accompanied by a mysterious *cough*hot*cough* bishounen. The story also is similar with both solving crimes and awesome action scenes. Furthermore,they both do not have parents that they're close to,resulting in their personalities are quite a bit cold (although Rahzel is very cheery with Alzeid) and they both are clever like dangan romps smart goddam