Onyx is 4’8, with a slim figure, and a graceful posture. Her skin is pale, her eyes are a dark grey, and her hair is black and straight. It falls just below her shoulder and is normally neatly braided back or pinned back. she has sharp features even though she is still young. Onyx normally wears dark and well-maintained clothing showcasing her blood status.

Quiet, analytical, and self-composed, Onyx is a listener rather than a talker and never acts impulsively. She is a keen observer, a patient person, and a careful planner, with a dry sense of humour, which comes out only when she is with people she trusts. Although she is a shy person, she is very loyal. Reading, strategy games, and baking are among her favourite things to do.

Onyx Merrick was brought up in an established wizarding family in the university town of Oxford, where magic was a private and controlled aspect of life. The Merricks respected tradition, learning, and control; magic should be understood before it was displayed . Onyx was brought up with spell books and magical artifacts that had been carefully preserved and used in a controlled and thoughtful way. Onyx was tutored at home in a small private class for magical children, with a strong education in reading, writing, and arithmetic, as well as magical history—but no spellcasting.

She was made aware from an early age about the kind of behaviour is expected of her as someone with the family name. Although she was never treated sternly, she is encouraged to think critically, to speak measuredly and to observe carefully before acting.

The first occurrence of magic for Onyx happened unintentionally when she was eight years old, in the city of Oxford. This took place during a moment of personal frustration as she was concentrating on her studies when her inkwell tipped over and miraculously stopped in mid-air and settled onto the surface of her study bench without a single drop of ink spilling,