"Words do not express thoughts very well, everything immediately becomes a little different, a little distorted, a little foolish," quotes one Nao of Brown character from Hermann Hesse, summing up why the graphic novel is the ideal medium for expressing the thoughts of young English-Japanese illustrator Nao Brown. Returning to London after a sojourn with her alcoholic father in Japan, the pathologically introspective Nao is trying to cope with professional and romantic rejection, as well as a form of OCD that manifests itself in murderous fantasies. On a single page, Glyn Dillon can depict the nuances of Nao's enigmatic facial expressions as well as the livid tumult beneath, the triggers of her rages and the storms themselves, and he does so beautifully.

Dillon emerged as an artist via his elder brother Steve Dillon's comic magazine Deadline, then was poached to be a storyboarder for film and TV for some 15 years, before embarking upon The Nao of Brown. Painting every frame himself resulted in a severely strained hand and a spell in hospital for nerve damage, but also, on the plus side, an uncommonly gorgeous graphic novel. Translucent watercolour exteriors  rain-soaked north London towpaths and gasworks have never looked prettier  abut the brighter and bolder interiors, in which Dillon has exactingly captured the Japanese collectable toys in the Kidrobot-alike shop where Nao works; a more hard-edged digital technique characterises episodes of the folkloric story of Pictor, half boy, half horse chestnut, that reflects Nao's own. Dillon's stylistic diversity is further displayed by his clever take on a classic Japanese woodblock print with a washing machine spilling socks into the foaming sea, as well as the thangkas at the Buddhist centre to which Nao retreats to calm her psyche, unsuccessfully.

Romance arrives in the unlikely figure of Gregory, a burly, middle-aged, washing-machine repairman who drinks too many pints, peppers conversation with poetry and Latin mottoes and knows all about the same Japanese spiritual and cultural references that Nao values. This incongruous trait reinforces the impression of Nao's self-absorption: characters with whom she concerns herself share her tastes or world view and she is unaware of or aggravated by those who do not. The feelings of others are clear to the reader, but barely register with her. Nao's mental condition is sparely communicated, Dillon having been intent upon portraying OCD subtly, without well-worn signifiers such as frenzied hand-washing or repetitive rituals.

However, having followed Nao's thoughts so closely and circumspectly, there is an unwelcome change of pace towards the end, when she reaches a cataclysmic point in her relationship and mental health. Rather than showing how the aftermath unfurled, in the careful manner of the rest of the book, there is a sprint finish to a conclusion that feels too pat. But, given the painful condition of Dillon's hand by this stage, I'm willing to forgive him.

Graphic novels are peculiarly suited to the discussion of Buddhist themes. That frozen moment in each pane, paused for us to examine, more details revealing themselves the harder we look, has something in common with meditation and the desire to appreciate the "nowness" of each moment of life. The Book of Pages by David Whiteland is a wonderful meditation on Buddhism and technology, and Deepak Chopra has produced a comic book about the Buddha.

The Nao of Brown is an engrossing and beautiful addition to the list. Nao is a charming half-Japanese woman with a bob and cute shoes, who works in a shop selling Japanese ephemera. She's obsessed with a set of Japanese comics called Ichi (Dillon has built a dedicated Twitter account and website), and falls in love with a washing-machine repairman who looks like one of the characters, bearded father figure Nobodaddy. She's an artist. She rides a bicycle.

She'd be a tooth-achingly sweet "pixie dream girl" if she didn't also suffer from sudden, invasive, compulsive thoughts of harming other people. Graphic novels excel at moving smoothly from the internal to external world, combining the action and intensity of a movie with the access to inner life of a novel. When Nao's sitting in an aeroplane, we see her vision of herself opening the emergency door. When she's confronted by a pregnant woman, she's overwhelmed by thoughts of stabbing the swollen belly. We, like Nao, are sometimes initially confused about whether she's really done these things or not.

Her meditation, therefore, and her interest in Buddhist drawing, aren't just an adorable pastime  she feels constantly on the verge of breakdown. Dillon's illustrative style is clear and crisp, but incredibly expressive; the motion of Nao's shoulders, the tilt of her head as she's talking, let us know that she may be about to have another compulsive episode.

The book is very funny about the experience of learning meditation and Buddhism  however hard we try to rise above ourselves, we're always irritatingly anchored, and the beaming faces of the slightly over-keen teachers at Nao's local meditation centre tell the reader it's OK to laugh, even while Nao is taking it all extremely seriously.

Nao's story is interspersed with the elliptical tale of Ichi character Pictor, a half-man, half-tree creature who, despite having a conker for a head, goes off to join the army. The rich, illustrative techniques of the Pictor pages, with their nods towards the decorated margins of a medieval Book of Hours, form a neat contrast to Nao's story. We can see why Nao might be drawn to these strange, serene images with their intricate detail demanding close examination.

The style contrasts, very deliberately, with the sketchy, sometimes impressionistic, illustration of Nao's own story. The narrative is meandering and thoughtful, taking in Nao's flatmate, her family and her friend and boss at the toy store. There's a light plot: Nao fails to see that her friend is in love with her, and her relationship with the washing-machine repairman is inevitably threatened by her OCD.

The end reads as Hollywood romantic comedy in a way that's unworthy of what went before. But then, as Buddhism would tell us, to focus on the destination is to look in the wrong place. The matter of life, and of a book, lies in the journey, not its end, and this novel is a very fine journey indeed.

 The Liars' Gospel by Naomi Alderman is published by Viking.