Tracy Mercer is the wife of Hands of Asclepius CEO Patrick Mercer and mother of Heather Ross. An accident several years ago left her in a coma. Fed up with the futility of bringing her back from her coma, Patrick engages in GUILT research and develops the four strains of Neo-GUILT, hoping that one would be able to awaken Tracy from her coma.

In the events of Under the Knife 2, Patrick attempts to revive her with Bythos, and after failing, activates Aletheia within Reina Mayuzumi as a last-ditch attempt to save Tracy. Following the end of the threat of Neo-GUILT, Derek Stiles goes off to meet a cranial nerve surgeon, perhaps to find a better way to awaken Tracy.

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