Her voice actress is Minako Kotobuki (Japanese) and Shelby Lindley (English).
Tsumugi, who often goes by "Mugi", is the gentle and sweet keyboardist of Ho-kago Tea Time. Mugi is a wealthy girl who has a sweet and gentle personality. Mugi is considered a piano prodigy since she was four and has experience, having won piano recital contests. She is the daughter of a company president, and her family has several villas in various places around Japan (and even one in Finland, much to Ritsu, Azusaand Ui's surprise when they tried to contact her at home). She often brings sweets and confectioneries to her friends. The tea set and the tea which they drink often are unusually high in price. Although she is a sweet and gentle girl, she is often entranced by the sight of two girls interacting closely together, sometimes imagining something more risque. She originally intended to join the choir club, but after Ritsu Tainaka's false flashback of promising to start a band and seeing Ritsu and Mio Akiyama's silly interaction, she decided to join the Light Music Club instead. Mugi displays a rebellious streak occasionally, due to her wanting to deviate from her wealthy nature, and diverts from a well-behaved and mature demeanor to the surprise of others. She also has a habit of getting a little too enthusiastic about experiencing new things that the others take for granted (such as ordering fast food, eating yakisoba at a festival, and purposely provoking Mio to hit her), since she has little opportunity to experience them with her high status.
Despite being wealthy, she tried her hand at a part-time job at a fast-food restaurant. While a lot of things do not bother her, she is fairly conscious about her weight (just like Mio), and she gets a bit anxious when her family's staff start spoiling her friends during villa visits.
Another characteristic that makes Mugi stand out from most girls her age is her surprisingly prodigious physical strength. Her astounding feats of strength include rapidly carrying Ritsu's drum set one by one with so little effort that she hummed a happy tune throughout, Instantly defeating the arm wrestling machine the Game Center on maximum setting that Ritsu had painfully struggled against, and sending Akira flying into the wall with a "light" slap. And this is not taking into account that she regularly runs in a brisk jog with her instrument, the Korg Triton Synthesizer, slung across her shoulder. (The Korg Triton is a hefty piece of equipment; at 17 kilograms it is comparable to a FIM-92 Stinger Missile or FGM-148 Javelin Missile Launcher.) Additionally, she was not slowed down or tired while dragging 30 kilograms of luggage while the band was running to catch a Taxi to London Heathrow Airport, all the while with the said Triton Synthesizer still slung across her shoulder.
Mugi has long, wavy blonde hair, sapphire-blue eyes, and a very fair complexion that the other girls lack. This hints at the possibility of being of European decent. She appears to have very thick yellow-brown eyebrows that remind Yui of pickled radishes.
Skirts over pants. High society lady styles, such as elegant one piece dresses.