Since the beginning of time, monstrous Demons and noble Guardians have battled for Earth - the everlasting gift of the one great Mother, creator of all life. A deep hatred burns between Demon and Guardian; the Guardians prevented the Demons from destroying humanity and the world itself. Eons later, Neo-Shinjuku City: few Demons or Guardians remain to continue their epic war. Humans rule the Earth, with no real memory of either Demons or Guardians. Yet deep within the dark underworld of the city, one supreme Demon is alive and plotting to subjugate mankind. Only one Guardian is left to do battle, and the fate of the human race is at stake. Based on the Graphic Novel "Twilight of the Dark Master (Shihaisha no Tasogare)" (Shinshokan) by Saki Okuse (Source: DVD Back Cover)

The world of Yozakura Quartet is actually not one, but two worlds: one of humans, and one of youkai. Despite appearing mostly human, youkai may have animal like physical traits, along with a number of special abilities. Normally youkai are confined to their world, but some have found their way into the realm of humanity. As a symbol of peace, and a bridge between the two realms, a city was constructed within the protective barrier of seven magical trees, otherwise known as the Seven Pillars. This city of Sakurashin is home to both humans and youkai, with the peace between them maintained by the Hizumi Life Counseling Office. The director of this office is Akina Hiizumi, a teenager with the inherited family ability to perform “tuning,” which can send harmful youkai back to their world permanently. He is aided by a group of girls, including the town’s 16 year old youkai mayor, Hime Yarizakura, their town’s announcer and resident telepath, Ao Nanami, and Kotoha Isone, a half-youkai who can summon objects just by stating the object’s name. As new residents enter and mysterious events begin to take place, this quartet of protectors and their closest friends must continue to guard the city of Sakurashin, and maintain the fragile balance of peace between humans and youkai.

Eiri Kurahashi is a Japanese art student who works in an antique shop. His friends begin to notice a dramatic, and rather concerning, change in Eiri, as he becomes more absent-minded and his behavior completely changes. They quickly decide to blame their friend's troubles on a girl. They may be right, however, as Eiri has begun seeing a beautiful, doll-like girl trapped within an antique Venetian glass that his uncle bought in France. She seems to be living in a strange other world, contained entirely inside this glass, but her image refuses to leave Eiri's mind. His sketchbook becomes filled with her likeness, and he realizes he has become completely infatuated with this strange little girl. When he recognizes her in a portrait by the mysterious Italian artist, Marchello Orlando, he learns her name is Cossette d’Auvergne, and that she was tragically murdered along with the rest of her family. One night, as he closes up the shop, he hears a voice asking him not to leave. Finally making contact with the object of his obsession, he makes a deal that he doesn't fully understand. [Written by MAL Rewrite]