IZ Books 4 which has the Combination and the cover is Hagun Seisenki.

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IZ Books 4 which has the Combination and the cover is Hagun Seisenki.
Title: Combination (コンビネーション) Author(s): Leeza Sei (writer/artist) Ageha Ohkawa (writer) Publisher(s): Kobunsha (Girl Comic) Year: 1991-1992 Volumes/Chapters: Vol. 6 Main Tags: Shounen-ai | Shoujo | Drama | Yakuza | Police | Mystery | Action | Violence Availability Online: partially available
The issue with Combination by Leeza Sei is that she continued Combination in 1996 with the plot written by Nanase Ohkawa despite removing Nokoru which appeared in Clamp School Detectives and using Characters she did not own but did not appear in CLAMP's work after splitting from CLAMP like Shuuko Imonoyama, CLAMP reused the plot from Combination for Card Captor Sakura, Tsubasa Reservoir Chronicles, and XXXHolic.
Combination was created by Leeza Sei, the illustrator and Nanase Ohkawa, the writer and it is Mokona that inked the first two volumes.
Fans assume that CLAMP allowed Leeza Sei to continue and gave rights to her but what happened proves otherwise as Combination went to hiatus after volume 6 in 2004 and Shogakukan did not serialize the continuation of Combination after volume 6 despite publishing the Omnibus in 2009 and Leeza Sei made it a webcomic/mobile comic and that webcomic/mobile comic disappeared and Leeza Sei's last manga in Akita Shoten's Princess, Tasogare no Rakuen(Twilight Paradise) ended in 2009 in Akita Shoten, and CLAMP reworked the plot and characters of Combination into CCS, TRC, and XXXHolic.
The reason why only Zyword and Mouryou Kiden remained in print is that the other works of Tamayo Akiyama released in English(Hyper Rune and Secret Chaser) cannot be released as ebooks as they made homage to other manga like that of Takeuchi and CLAMP, the same can be said for Cluster and Shade which also has homages, but Derayd which was originally published under CLAMP is clean, Shade, Cluster, and Derayd never got licensed.
The same can be said for Leeza Sei's works in Akita Shoten as they have homages to CLAMP's works but the issue with Leeza Sei (Iba Takeo) is that she continued Combination with CLAMP not wanting it continued as Ohkawa had reused the plot of Combination and also reused elements of Combination to CCS and Holic, the sequel of Combination ended up overlaping or have heavy plot similarities in the volume 3-6 of Combination with Tsubasa RC's volumes 13(91-94), 17-22(136-174) and Chapter 2 of volume 1 of TRC and there has been difficulty in serializing Combination since the gap of the publishing of Volume 5 in 1999 and Volume 6 in 2004 and its permanent hiatus since volume 6 and the nature of Combination's continuation might have affected Leeza Sei's other works.
Evolution of Shuuko Imonoyama and Tomoyo.
Shuuko Imonoyama is the Imonoyama sibling created by Mick Nekoi.
The issue of the manga Combination aside from the fact that Leeza Sei using the plot and characters created by current CLAMP members without their approval on the continuation of Combination is that the plot of Combination spoils the plot of Tsubasa especially the Celes, Nihon, and the final arc of Tsubasa and certain parts of XXXHolic most notably chapters 136-174 of Tsubasa R.C., so continuing Combination could affect XXXHolic and Tsubasa because CLAMP reused elements of Combination in XXXHolic, Tsubasa, Card Captor Sakura, and their related works.
It is actually hinted on the publishing history of Combination that Kodansha and CLAMP actually did something as Combination is put into permanent hiatus but they did not do something that could come out publicly like suing Leeza Sei and Kobunsha and Combination's webcomic never got compiled into a book after it did not get serialized after its hiatus in Kobunsha but the fans are left in limbo about what really happened.
During the time when Combination's sequel was being serialized until 2009 or rather between 1996-2009 CLAMP was strict on copyright.
If Miracle You, Hagun Seisenki, and Cluster had succeeded as Media Mix projects or at least had anime adaptations and CLAMP’s aborted anime design project in 1990-1991 materialized, Leeza Sei and Tamayo Akiyama likely would not have left CLAMP in 1991/1992, but instead remained until 1996. In that scenario, they would have contributed to the creation of Magic Knight Rayearth which would have been different as a project in the manga side as they would stay until 1996. However, this would mean that X and Cardcaptor Sakura would never been made as far as I know in the 1990s we could have seen Shin Shunkaden and Clover continued by CLAMP in this scenario.