It all began with a floating leg.

Or, more specifically, an idea came tattooed on the leg of a woman kicking through the water in Key Largo, Fla., seen clear as day through Patrick Duffy’s diving goggles. Mr. Duffy, who ran a scuba diving therapeutic program for military veterans with his father, was inspired by the tattoo; it was her dedication to her late husband, a Navy SEAL killed in combat.

“In that moment, I thought, ‘Wouldn’t it be cool to turn that tattoo into a reliquary?’” Mr. Duffy said. “To put a piece of something she cared about, maybe even her husband, into the tattoo itself?”

Four years, a handful of dedicated colleagues and nearly a dozen patents later, Mr. Duffy has brought the idea to life with Everence, a product he and his partners hope will deepen bonds — in the most literal and physical way — between family, friends and loved ones.

It is about as biologically intimate as one can get. Everence is a powdery substance synthesized from a sample of DNA, something as simple as a few thousand cells from a swab of a person’s inner cheek, or from cremated ashes. A small vial of Everence can be brought to a tattoo artist and added to any type of inks.