Reimu is defined as unusually easygoing, lacking any sense of danger, and being carefree. She is described as simpleminded, always showing her true feelings and acting on whatever ideas she thinks at the top of her head. However, ZUN has also said that nobody except her can know what is in her head, and thus how she is depicted varies depending on the perspective, be it human, fairy, or youkai. She can also be emotional and noisy, and her presence is well known wherever she is, but she can also merge into her surroundings quite easily when necessary.

She is portrayed as someone simple who passes her days sweeping the shrine grounds, drinking green tea and lazing about; to the point that Kasen Ibaraki thought she lacked training to be the Hakurei shrine maiden and made her train to be more disciplined, something that only worked for a couple of days due to her easygoing personality. However, Kasen states that despite Reimu being "a little unreliable and a little slovenly", she still performs her duties, doing enough to be befit the title of Hakurei shrine maiden.

On the other hand, she is someone with an intuition when it comes to incidents, usually rushing to solve them and not letting anybody get in her way and waste her time. This leads to some people she confronts to think that she has an “indescribable intimidating aura”. This is backed up by her innate abilities, powerful enough to beat her opponents without her being worried of training often, to the contrary of Marisa Kirisame's.

Her straightforward and open personality makes her being liked by both youkai and humans, but she herself considers only few people her friends (like Marisa Kirisame) and she maintains a more strict stand against youkai due to her being human and the Hakurei shrine maiden. As she attracts the people she interacts with and she deals more with not humans than humans, her shrine gets more youkai visitors than human. Reimu tries to revert this and get more human followers and donations through various schemes, but they usually end up not working due to how simple and flawed were or because they were a product of a burst of her emotional side, like in Wild and Horned Hermit. In other occasions, those only end up attracting more youkai instead.

Although she says it is her job to exterminate youkai, she has worked with them in multiple occasions, such as during the incident in Subterranean Animism. She can be seen drinking and hanging out with youkai that invite themselves to the many flower viewings she hosts at the Hakurei Shrine, and collaborating with kappa with business at her shrine festivals. She even offered the three fairies to drink with her after reprimanding them for trashing her shrine, and later gave them several tasks to help clean the shrine. Toyosatomimi no Miko theorizes she only says it is her job to exterminate youkai as a way to say that she wants to maintain Gensokyo's equilibrium, something Yukari Yakumo and others remind her of when she gets too carried out dealing with youkai. Her friendliness with youkai did not stop Eiki Shiki, Yamaxanadu from saying that she exterminated youkai without reason, and that she slacks in basic shrine maiden activities like communicating with her own god.

While many inhabitants of Gensokyo are capable of flying, Reimu's ability extends beyond that; she is someone who excels at floating through life. Reimu generally displays extraordinary intuition and incredible luck, naturally ending up on the path of least resistance through most situations. However, when distracted or acting with impure motives she quickly loses her edge. On one occasion observers saw Reimu dodging an attack "like she was made of air" while Reimu herself saw the attack swerving to avoid her. On another Reimu unknowingly walked across a river without getting wet, by stepping on fish that swam beneath her feet. This ability has been represented in most of the vertical danmaku games since Perfect Cherry Blossom as a smaller hitbox. The ultimate expression of the ability is Innate Dream, which allows Reimu to float away from reality and become impossible to attack. This was considered too powerful for use as a spell card until Marisa gave it a name and time limit.

As the Hakurei shrine maiden, Reimu can handle the Hakurei Yin-Yang Orbs, and is trained in youkai extermination techniques as well as standard duties like performing blessings. Reimu is also capable of channeling gods, but she isn't well-trained enough to do so reliably.

Reimu displays great aptitude with magical barriers - among her techniques are barriers that explode, push enemies (or herself), or allow her to teleport. Reimu is capable of dismantling barriers and seals too complex for Marisa Kirisame and Patchouli Knowledge to understand, with what Marisa calls her "cheat technique".

It's stated in the omake.txt (おまけ.txt) of Embodiment of Scarlet Devil that Reimu can control the natural spirits of living things, an ability which isn't listed in any source afterwards. Reimu has been shown to be able to detect signs of a soul when it was alive in bones and remains.

During the events of Urban Legend in Limbo, and at least until the end of Antinomy of Common Flowers, Reimu acquired abilities based on the "Gap Woman" urban legend. This allowed her to open gaps similar to the ones used by Yukari Yakumo, which she used as portals for herself or to attack.

Reimu is the shrine maiden of the Hakurei Shrine. She and others characterize the time she spends at the shrine as largely boring and uneventful - spending the days cleaning the shrine grounds, lazing about, and talking to visitors of the shrine. While she is sometimes serious about her duties, the shrine is usually is not a very popular location for human worshipers. This is in part due to the amount of youkai that visit the shrine, to the point that, according to Marisa Kirisame, everyone in Human Village says that "youkai completely control [the] shrine", something Reimu is frustrated about. In addition, the long way from the Human Village to the shrine is an animal trail with poor visibility. However, Reimu still manages to attract sizable amounts of visitors with festivals hosted at the shrine - both traditional Shinto holidays such as Setsubun and non-traditional gatherings such as a "Stay Cool Festival". The festival stalls often have kappa and other youkai running them, and the revenue produced from them by visitors make up a valuable portion of the shrine's income.

In addition to her duties at the shrine, Reimu has the duty within the Human Village of performing exorcisms, stopping supernatural disturbances, and generally pacifying disorder arising from the villagers' fear of the unknown. Though she may not always know the cause or the solution behind a disturbance, Reimu still has no problem offering her services - she states that placing the incomprehensible in the context of the supernatural and then containing it to quell anxieties is "one of the most respectable duties for a shrine maiden to carry out".

Finally, Reimu specializes in youkai extermination as one of the main incident resolvers in Gensokyo. In most cases, "extermination" means non-lethal reprimanding, though Reimu will not hesitate to use sealing or lethal measures against youkai that cannot abide by Gensokyo's rules. A prime example is the fortune teller, who became a jinyou (human youkai) after using a taboo method causing a panic directly inside the Human Village, leading to his swift, permanent extermination. Reimu believes that jinyou would destroy the balance of Gensokyo, which is why she keeps careful watch over Kosuzu and certain other humans at risk of becoming youkai. Yukari Yakumo describes Reimu's job as not being that of a youkai exterminator, but rather a "balancer between humans and youkai", who prevents youkai from attacking humans and humans from becoming youkai.

In most of the Touhou games, Reimu uses the Yin-Yang Orbs, go-shintai of the Hakurei God, in combat. Kasen Ibaraki states that the shrine's blessing is youkai extermination, which is manifested through the Yin-Yang Orbs. In Subterranean Animism they also functioned as communicators with people above the surface.

Reimu utilizes a gohei, sometimes referred to as her purification rod, originally prepared by Rinnosuke Morichika. She uses it for Shinto rites and exorcisms, as well as in combat as a melee weapon.

Reimu possesses a great amount of ofuda, sacred paper charms with anti-youkai properties that she uses to fight, seal or exterminate youkai of any kind in her danmaku. She can also use them to create barriers and even copies of herself. Like the Yin-Yang Orbs, she uses them in most, if not all, games she has appeared in, either as a normal shot (usually with homing properties) or as bullets for her spell cards.

Reimu also utilizes a large collection of large throwing needles hidden within her sleeves in combat, which she chooses because of their divine connection and because they are easy to throw.

She has brown-black hair which varies in length and style between games (tending towards long and loose in later works), and her eyes vary from brown to red to even blue depending on the game, but she still wears a red ribbon and matching tubes on her sidelocks. She's still seen in her "shrine maiden uniform", but it now bears little in common with the standard uniform beyond the red-and-white color scheme, something ZUN has acknowledged. This uniform consists of a red skirt (rather than the standard hakama), a sleeveless red top with a white collar, tied with a yellow, red or blue ribbon depending of the game, and a pair of white detached sleeves which exposes her shoulders and sarashi. Due to the color scheme, she's occasionally called the "red-white shrine maiden". Her shaman clothing and her purification rod came from Rinnosuke Morichika, but it's unknown who designs them.

Marisa is a close friend of Reimu. They are seen together most often in the print works, game and extra stage prologues where they hang out at the shrine together, chatting about the latest rumors and news in Gensokyo. Marisa even helped Reimu in her festivals before.

Reimu and Marisa often quarrel and spar with each other, for reasons ranging from resolving incidents to hotpot ingredients. Those fights can end up in a danmaku battle like in the Stage 4 of Imperishable Night or their battles in the fighting games. Regardless, they usually resolve their differences and continue being as close as ever.

They've also worked together on numerous occasions, such as when they chased down an enenra, or worked to exterminate a vengeful spirit. However, they usually solve incidents at their own pace, and Marisa often aims to solve incidents or events before Reimu.

Despite being a youkai, Yukari occasionally seeks Reimu's assistance in resolving incidents and maintaining order in Gensokyo, such as in Imperishable Night, Subterranean Animism and Antimony of Common Flowers; as well as mentoring Reimu such as to push her spiritual powers to invoke the gods in Silent Sinner in Blue, chastising Reimu on proper god worship such as in Strange and Bright Nature Deity and informing her of how the boundary effects objects from the outside world such as in Oriental Sacred Place. She remarks about compensating Reimu accordingly during the Imperishable Night incident.