Anime First: Well, OVA first, but a manga adaptation came out later in the year.
Artifact of Doom: All of the objects that were splashed with Cossette's blood the night she died; a mirror, a piano, a clock, a bisque doll and a glass cup. After her death they became cursed with a deep grudge against her murderer, and kill all of their subsequent owners.
The Atoner: Eiri is forced by Cossette to become this, bearing the punishment and pain for what Marcello did to her simply because he can see her spirit and, like Marcello, fell in love with her. He eventually grows to accept this , at which point she begins to regret it due to seeing Eiri for who he really is.
Failure Is the Only Option: In the manga, Eiri must die to free Cossette's soul. He runs back at the last moment and lives, but as he leaves the hospital, a truck hits and kills him. Cossette then shows up and implies it happened because he didn't love her enough to die for her, and now she must wander the world in search for his next reincarnation.
Fortune Teller: Michiru frequently borrows space in Eiri's antique shop to do tarot card readings.
My God, What Have I Done?: Cossette comes to greatly regret the pain she causes Eiri, and the third OVA begins with her farewell to him before she apparently crosses over. Unfortunately, her departure only makes things worse...
Eiri is Marchello's reincarnation and falls for Cossette's spirit.
in the OVA, Cossette gets to reincarnate in Shoko.
Ret Gone: In the manga, Eiri's existence is slowly disappearing as the night of the ritual to free Cossette gets closer, because he's still willing to join her in death. Once he escapes from Cossette dragging him to hell (actually from a church on fire), everything goes back to normal.
Sadistic Choice: In the manga, Eiri finds out that saving Cossette will result in his own death. Caught between fear and love - and life and death - he must make up his mind about whether or not he loves her enough to sacrifice his life for her.
Together in Death/You Are Worth Hell: In the manga, the only way to free Cossette's soul from her painting is for Marchello's reincarnation (Eiri) to kill himself in a ritualistic way and join Cossette's soul in hell.