Tsuki Fujiwara was a 18 year old Japanese high school student having just started her final year. She lead a very upbeat, optimistic life with aspirations to get into the best college she can. In her spare time, she joined the literature club to learn about folklore from all over the world. She became fascinated by rumors that the disasters of the 90s were caused by a battle between supernatural beings.
On the way home one day, she got sidetracked into an alleyway and witnessed two mysterious creatures battling one another: a Kami and an Akuma. The Kami was injured and on the verge of death, but bravely, Tsuki intervenes. The only way for the Kami to survive would be to meld itself with Tsuki, thus embodying her with magical powers such as an awareness of the spirit world and most visibly - the ability to channel energy from the spirit world to perform extraordinary feats. The Kami revealed its name to be Shiro and guided Tsuki into facing against the Akuma. They end up defeating it, but Shiro being too injured, cannot leave just yet. Shiro needs to use Tsuki as a vessel to recover in, but he insists that she can’t tell anyone of her newfound abilities.
In spite of Shiro’s request to keep a low profile, Tsuki realizes the potential of her powers to help people. Together, Shiro and Tsuki could take on the Akuma to protect others. Thus, Tsuki dons the identity known as Yoru-chan putting together a costume to go with it. She decides to take up fencing and martial arts to improve her athletic abilities to be more prepared against the strenuous workload that fighting an Akuma could be. By day, she’s a high school student, and at night, she fights Akuma as Yoru-chan.
However, Tsuki comes into conflict when she witnesses a mugging. Shiro highly advises that she doesn’t intervene because it’s not her business. Tsuki is only supposed to be fighting Akuma, but Tsuki pleads that she has no choice. She sees someone and has to help them. Despite Shiro threatening to withdraw her powers, Tsuki rushes in anyway to stop the mugger. Shiro, not wanting to abandon Tsuki, decides to assist her by providing his power.
Tsuki intervenes to stop the mugging, and she even brawls with the mugger. Even after being threatened with a knife, Tsuki fights back. A nearby witness however catches the incident on camera and uploads a video to the Internet. A few of Tsuki’s abilities were caught on video, and the incident went viral. She was all over local news, and became an Internet sensation - some people split on whether or not her powers were real or fake. Now the world was expecting more of Yoru-chan. Akuma were no longer her only specialty. She had to fight real world crime. And over time, she grew a reputation as a mysterious vigilante rumored to have special powers.
Over the next few weeks, her actions draw the attention of a powerful sorcerer codenamed the Voidmancer. He was a philosopher who closely followed the Antithesis Event of the 1990s and came to the conclusion that the light and the dark were meant to cancel one another out. The world was off balance because light prevailed in the end, and thus, it needed more darkness. He set about to bring a hidden supernatural war between the Kami and Akuma. Seeing Yoru-chan, the balance of light and dark, as the possible key to his experiments, the Voidmancer wanted to capture her.
After multiple failed attempts, the Voidmancer decided to send one of his best minions - the Nekomata. The Nekomata did something rather unorthodox and declared a public challenge to Yoru-chan, believing it can be a way to draw her out. After the Nekomata threatens some civilians, Yoru-chan has no choice but to intervene. Thus, the two engage in a battle out in public for the world to see.
Yoru-chan defeats the Nekomata who submits and offers to be her ally. Though suspicious at first, Yoru-chan accepts believing she can learn more about the spirit world from him. However, the Voidmancer wants the Nekomata to act as a double agent, to learn her secrets so that the Voidmancer can capture her.
For Tsuki herself, the battle with the Nekomata soon made her into a celebrity and a true Internet phenomenon with new merchandise and invitations to talk shows. Sooner or later, people began to guess at Tsuki’s identity.
Tsuki soon runs into difficult maintaining her double life. She gets stretched very thin maintaining her studies and her vigilante work. Eventually, she becomes worried for her academics. The Nekomata lends a hand in her studies and the two grow a bit closer with Tsuki still being unaware that the Nekomata was still in contact with the Voidmancer.
While Tsuki still manages to keep her secret identity, things get complicated when other superheroes bonding with Kami come to light. News stories from all over Japan tell of more gifted individuals fighting against both criminals and mysterious shadows. Shiro becomes concerned that his kind is losing the war with the Akuma and more Kami are being forced to bond with humans to survive. Not only that, Tsuki’s battle against the Nekomata invited more powerful adversaries to challenge her making Japan a supernatural battle arena.
As summer vacation approaches, Tsuki makes it her mission to meet up with these other heroes.