text: Critical response to the series was generally positive. An Anime News Network reviewer, Theron Martin, wrote that although the setting was unclear, its narrative and cast were appealing. Reviewers have pointed out that the fight scenes and the handling of the Contractors contrasted with the more-lighthearted parts of the narrative. The series' final episodes received mixed reviews; Hei's character arc and his relationship with Amber and Yin were praised, but the ending was considered rushed. According to an Active Anime reviewer, most of the characters were generally three-dimensional and the narrative was compelling. A retrospective Fandom Post reviewer said that the series subverted viewer expectations because it aired in the same time slot as the popular Code Geass with appealing characters and fight scenes. Fans were disappointed by the ending's lack of resolution, to which character designer Iwahara responded with his manga Dimension W. An AnimeNation reviewer said that the series was less popular in Japan than the West, and the Japanese audience was surprised by a sequel. The series has been compared to X-Men comics for its handling of supernatural fighters, and to Cowboy Bebop for Hei's enigmatic characterization and stylishness.
  The series' Japanese and English voice acting was praised, although Fandom Post suggested that deliveries were better executed in later episodes, while DVDTalk suggested the English dub for better immersion into the narrative. Tomoko Kawakami's performance as Amber, the actress' final work before her death, was called "solid"; Jason Liebrecht's Hei was described as "a schizophrenic variation" of Syaoran from Tsubasa: Reservoir Chronicle. Anime News Network said that the Japanese and English voice actors synched well with the video. "Howling" by Abingdon Boys School and "Tsukiakari" by Rie fu were good contrasting themes in the series. The second opening theme, "Kakusei Heroism" by An Cafe, was praised; "Dreams" by High and Mighty Color was said to lack the appeal of the first ending, "Tsukiaraki". Yoko Kanno's score was described as "unintrusive" by Ain't it Cool News for the variety of instruments used for background music while Anime News Network commented it "achieve[d] a sort of synergy, pouring their considerable skills into a sequence of silent beauty and power".
  In the two manga, Hei played in the other manga spin-off by Nokiya was criticized by MangaLife as "flat".