Kuroshitsuji, Karneval Recommendations
Both have a younger boy as a main character. Both stories focus on the relationship between the main characters. Both are mainly mystery shows with some fighting. Both are kind of gothic but Karneval has a more Circus feel. Both are really good.
If you're into supernatural fantasy is part of your vocabulary, then Kuroshitsuji (Black Butler) and Karneval are definitely something to look into. For its colorful cast of characters also come a fascinating setting with vast potentials. There are supernatural elements present in both series inspired by the premise and gimmicks. The main male protagonist from both series contrasts a bit differently however but their relationships with others are cleverly crafted. Similarly, their stories offers many glimpses at plot twists with attractive mystery elements to keep you at your seat.