Sley serves as the secondary operator aboard the trading ship Glomar, taking command whenever the captain is absent or manual control is required. He is engaged to Mimsy Laaz, a young Emaan girl nearing the end of her fertile period—a matter of cultural importance, as Emaan women are expected to marry and bear children before infertility occurs around age eighteen.

He harbors a powerful resentment toward Kei Katsuragi, whom he blames for drawing the attention of the militant Chilam faction. This pursuit results in grave danger and the deaths of multiple Glomar crewmembers. Sley’s animosity is intensified by Kei’s nature as a Tokuiten, or dimensional singularity, which makes him a target, and by Kei’s romantic involvement with Mimsy, positioning the two men as rivals.

Despite his personal grievances, Sley demonstrates genuine concern for Mimsy’s welfare. Out of respect for her autonomy, he eventually accepts her feelings for Kei, choosing her happiness above his own.

Through the series, Sley grows more assertive, partly influenced by Kei’s own urging that he take a more active role in protecting Mimsy. He ultimately decides to formally marry Mimsy and conceive a child before her fertility ends—a choice Kei supports, recognizing their compatibility.

Sley dies early in the story, sacrificing himself heroically.