If you liked the Higanjima manga, the Anime-Planet community thinks you'd like:
Itsuki Kamiyama is a young man in high school who is morbidly obsessed with murders and death; he even combs through the paper for new information about killings. One day when he notices his classmate Yoru and the scars on her pale wrist, he sees that she too shares his interest in death. Together, the two of them manage to solve a string of murders - not for any sense of justice, but rather out of curiosity. Yet, when does it get to be too much? And what happens when Itsuki stumbles upon a dark secret from Yoru's past?
I don't know why exactly, but the darkness in Goth reminded me of the dark and sinister feeling of Higanjima. Though Goth is about two death-obsessed teenagers who solve crimes out of sheer curiosity and "fun" and Higanjima is about vampires, both bring darkness and evil to the table. If you like Goth, maybe you'll like Higanjima as well and vice versa.