The second season of Jigoku Shoujo retains the same dark and moody elements of the original JG even as it explores the interaction between Ai and those who seek her services. This forging of bonds between doomed supernatural females and humans is also very present in the latter episodes of Vampire Princess Miyu. Jigoku Shoujo Futamori reveals a deeper kinship between Ai and Miyu, firmly establishing them as kindred spirits.
Boogiepop Phantom and Jigoku Shoujo deal with people in extreme situations and mysterious entities with a dubious role within the narrative. BP's plot is extremely confusing, with episodes retelling the same event and doses of introspective speculation; while JS is considerably easier to follow, with a mostly episodic structure. They share a very dark mood and are pessimistic for the most part: these series are a window into insanity and its devastating effects; the supernatural elements are fully incorporated in acute human dilemmas.
-people who are cornered and have to turn to paranormal for relief.
-which in turn only causes huge huge. HUGE. problems for society.
-we're talking, freaky freaky escalation
-there's also a poor heroic truth seeker
JSF and KnK have a lot in common. Both have stunning production values, and are downright beautiful to watch. Also, both have excessively tsundere main characters (Enma Ai and Saiki, respectively). Both deal with the supernatural and hauntings, as well.
Both of them concentrate about death. Jigoku Shoujo is sending people to hell and in Shigofumi you recive letters from dead people. Both tells not only about main characters but also about random people and their problems, for example bullying. Jigoku Shoujo has every episodes in creepy climat, Shigofumi has half of episodes like this.