Like the other Phantomhive servants, she has a great deal of respect for, and a slight fear of, Sebastian Michaelis. She also seems to have a bit of a crush on Sebastian, frequently blushing and becoming even clumsier when in his presence. She is also exceedingly loyal to Ciel, and does her best to please both.
She is an exceptionally clumsy maid, frequently falling or knocking things over, breaking many of the manor's things as a result. According to Sebastian, her idiocy is the problem and not her poor eyesight. He also states that he has heard that clumsy maids have charm, but not that he can see. He adds that she makes him recall what murderous intent feels like.
She is notable for being extremely superstitious, but does not seem to let her superstitions frighten her, as she states that she has a soft spot for scary stories.
Mey-Rin has dark purplish-red hair and wears thick, broken glasses that hide the color of her eyes. In the anime, when her eyes are shown, they are a yellowish-brown color but according to Yana Tobosos's drawing of Mey-rin her eyes are red. Her hair is actually rather long, but she wears it tied up high on her head. She wears a typical maid's outfit, including a lacy frill worn in her hair, blue dress, and white pinafore with ruffles around the shoulders and blue buttons. She also wears lace-up, knee-high boots. During her days as a sniper she appeared to have longer hair, and wore in all black outfit of shorts, a sweater, and tall boots up to her thighs. She is 165 cm (5'5") tall.
Little is known about Mey-Rin's past other than that she used to be a sniper, and as a result, can wield high-powered rifles like hand-guns. It is not known why she came to work for Ciel, but she seems pleased to get to wear skirts and the glasses he purchased for her, which is part of the reason why she does not buy new, unbroken glasses. Without them, she is able to see great distances clearly, aiding in her ability to be a sniper.
In the anime, it is shown that Sebastian recruited her to come work for Ciel, which she agreed to, likely because she was shown to be disturbed by some of her assassination missions.