Ayu is the same age as Yuichi, but acts younger. She often uses the word "Uguu" when she is upset or mad. Ayu is the main female character in the anime although it may not appear like that initially. Her favorite food is hot Taiyaki.
She is voiced by Yui Horie in the Japanese version of the anime, and by Brittney Karbowski in the English version of the anime.
Ayu is very small for her age, and is short. She has short reddish-orange hair and reddish eyes. She is always wearing a yellow coat and a backpack with angel wings on the back. She also wears a red head-band.
When she was younger she wore a white head-band with a bow at the end. Most of the time she has a yarn sweater with a blue skirt.
Ayu is a strange and mysterious seventeen-year-old girl, the same age as Yuichi, though due to her short stature at 154 cm (5'1") and comparatively low body weight at 41 kg (90 lbs), she is perceived initially by Yuichi to be much younger; in fact, Ayu is the shortest and least heavy character introduced in Kanon. Ayu's three sizes are 80 cm - 52 cm - 79 cm (31" - 20" - 31"), and are the closest to Shiori's despite Shiori being one year younger. When first introduced, Ayu is seen wearing a large tan duffle coat over a sweater and shorts, despite the cold winter weather, and is the only Kanon character seen to regularly don mittens. On her feet, she wears brown argyle socks and snow boots. She is immediately recognizable by the red Alice band in her short brown hair, and a small backpack she wears which has two attached wings on either side. In later appearances, she is sometimes seen without her coat or mittens. As a child of ten, Ayu is depicted wearing a pink sweater, a short skirt, and a large white bow in her hair, which is grown-out slightly longer than when Ayu is seventeen.
Ayu is a very childish but sweet girl at the same time. She was once described by Yuichi's aunt as "One big bundle of energy". Ayu is also a very clumsy girl. She is terrified of ghosts, evil spirits and scary movies. When she is upset or sad she says "ugū". Since childhood, Ayu has referred to herself with the masculine pronoun boku (僕?)—Japanese for "I", a rare occurrence among females. Ayu is notorious for her catch phrase, "ugū" (うぐぅ?), which she mutters as an expression of various negative emotions such as frustration, anger, and fear. Her favorite food is Taiyaki, and she is seen eating the confection many times throughout Kanon. Ayu comes off as somewhat strange, such as initially tackling Yuichi and yelling his name whenever she would spot him. These tackling fits eventually diminish in severity to simple taps on the back as time goes on or even simply calling out his name when appearing seemingly out of nowhere behind him. She can be clumsy at times, and is prone to tripping. Ayu tends to be naïve about common things, such as not knowing what a mobile phone is, but enjoys learning about new things. Yuichi quickly discovers how terrified Ayu will become at even the mere mention of ghosts or demons. When put into an uncomfortable situation, such as having to walk alone at night, she is noticeably jumpy and is prone to screaming. She is left-handed.
- Ayu's zodiac sign is Capricorn.