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After graduating from the Kubert School, Warren spent a year attempting to acquire the rights to produce a comic based on the Dirty Pair. He was finally able to make inroads with the help of Toren Smith and Studio Proteus, who had connections in Japan. Warren put together a portfolio of "Dirty Pair"–related work which Smith then took to Sunrise Studios, but they were unimpressed with the work and negotiations went nowhere. Smith then contacted Takachiho Haruka, the creator of the "Dirty Pair", directly. Haruka was much more impressed with Warren's art and Smith's ideas and agreed to license the characters for an American comic. This directly resulted in Warren's first major work, "Dirty Pair: Biohazards", which he co-wrote with Smith and published through Studio Proteus and Eclipse Comics in 1989. The next two Dirty Pair works would be co-written with Smith and released by Eclipse Comics. Starting with the fourth book, "Sim Hell", it became a solo project and was released by Dark Horse Comics.