The character of Sunako is very self-conscious, and has a fairly bad self-image of herself. She frequently calls herself ugly, and never acknowledges herself as a beautiful person. Most of the time she can be found in dark spaces or areas that are believed to be haunted.
At the same time, the author shows that Sunako also has very strong convictions. This could range anywhere from defending her fellow characters to refusing to do anything she dislikes, such as dressing up. It is frequently shown in both the anime and manga, however, that Sunako has no problem compromising some values (i.e. dressing up) in order to further her own ends. Sunako's fascination with all things dark and morbid resembles that of the story's creator, albeit in a more extreme form.
A constant theme of Sunako's personality is her view of beautiful and ugly people. She sees herself as ugly, while viewing characters such as Kyohei or Noi as incredibly beautiful. Sunako's belief appears to be that while beautiful people can become ugly, ugly people can never become beautiful. In the manga Sunako often reacts violently to the presence of beauty, believing that ugly people such as her should stay in the darkness. However, the problems with Sunako's retreat from the world is that it limits her capacity for life, as well as keeping her from fairly viewing all that is around her. It can be suggested that by Sunako adopting such a severe viewpoint on "ugly" and "beautiful" people, she has become exactly the type of person that she despises. One such character similarity can be seen by comparing the person who dumped Sunako at the beginning of the manga, and Sunako herself assuming that Kyohei couldn't understand her due to his beauty.
Most of the time Sunako can be seen in super deformed mode. However, whenever she is in a situation where her inner beauty comes forth, she almost magically transforms into a beautiful young woman, much to the surprise of many onlookers. Sunako's inner beauty frequently emerges whenever her character's viewpoint is challenged, causing her to change her belief system about beauty and humanity in general.
At the beginning of both the anime and the manga, Sunako is seen confessing her love to a faceless classmate, only to have him rebuff her cruelly, stating that he hated ugly girls. Since then the character has thrown off any scraps of femininity that she may have possessed, believing that it is a waste of time. Throughout the series so far Sunako has held to the belief that she is ugly, and is a "creature of the darkness". Her aunt, fearing that Sunako's unladylike ways are not only limiting her at life, but also at love, bribes four young men with a promise of free rent if they can perform a Pygmalion-esque makeover on Sunako.
For most of the manga and anime Sunako's time is spent both avoiding yet caring for these young men, as it is shown that they are almost completely incapable of performing everyday maintenance. As the storyline progresses Sunako begins to recognize beauty, even remarking that roses are pretty. So far in the manga Sunako's back story has yet to be fully revealed, but it is unsure if her fascination with the morbid and dark began with her transformation or if it was a hobby she had even before. In the anime, it is hinted that her fascination with things morbid began as a junior high student, perhaps some time after she was rejected by the mystery boy. Her mother however has let her daughter do whatever she wants, even going as far as helping Sunako hide her disturbing collection from her horrified father. As Sunako progresses in her unwilling makeover, she begins to realize her own self-worth and beauty, as well as the effect her actions have on other people, such as her aunt.
In Chapter 62, she finally is able to confront her past and her friends at a school reunion, including the cruel classmate. With that confrontation, she is finally able to move on, realizing that she has a new life and new friends.
Previously, Sunako went out of her way to avoid any person that was exceptionally beautiful, or a "creature of the light" (mabushii ikimono
まぶしい生物 "dazzling creature") as the character would put it. Her few friends were extremely unusual, such as the granddaughter of the abominable snow woman or Sunako's Granny. Since her roommates are quite attractive, Sunako has attracted good and bad attention from the female population, with most of the initial reactions ranging towards the negative side. Sunako has made a few female friends such as Noi, Takenaga's patient girlfriend. Her remarkable athletic and domestic abilities eventually win over her classmates, though Sunako notes to Yuki that she is able to get along with them because she makes an effort to do so rather than through natural ability.
Sunako is mostly unable to directly view any attractive male in fear of massive nosebleeds. (Nosebleeds are frequently used in anime and manga to show physical attraction, usually to comedic ends.) Strangely enough, this feature has actually been met with affection from some of her roommates, such as Kyohei, who often uses it to his advantage when he sees fit.
Despite Sunako's growing tolerance for beautiful boys, as well as her slow opening to the world, Sunako does not pursue romantic relationships. She has a growing fascination with Kyohei, as he is the one boy who most closely resembles her in personality. Despite the observations of passers-by, both parties claim that there is no attraction to each other. However, as the series progresses, both begin to see each other in different lights as previous assumptions are proven wrong. Though she does not seek a relationship, her relationship with Kyohei grows to where they seem fond of the other though they may not know it.
In volume 18 Kyohei surprises Sunako with a kiss. Although Kyohei claimed the kiss was an act of confusion, Sunako realizes that she doesn't hate Kyohei, and doesn't find him as radiant anymore.