Thirteen

"'The owner of the reaper's cave, Thirteen has been acquainted with Solomon for over a thousand years, and often competes with him in games for his soul. She always names the traps she makes for fun, and you can say the naming is rather unique.'"

Thirteen is first mentioned as simply "the reaper" in Lesson 35-5. She is a powerful entity that watches over the "life candles" that represent the souls of humans, demons, and angels. Her first proper appearance is in Lesson 65-3.

Appearance
Thirteen is a reaper with pale skin and long, colorful hair parted in the middle. Her hair starts pink at the roots and turns purple and blue further down. Her eyebrows are also blue. Her eyes are vaguely reptilian in appearance due to her vertical pupils. They are lime green with a pink gradient. Thirteen is also visibly wearing makeup: eye shadow that matches the colors of her hair and red lip gloss. On her hands, she wears yellow nail polish.

Personality
As seen in the Devilgram Battle for the Bread!, Thirteen isn't the strongest singer. Asmodeus comments that she's "completely tone-deaf."

It seems that Thirteen has a dislike for angels. She refers to Raphael in Lesson 65-9 as an "arrogant, self-important angel," and in the same lesson Diavolo remarks that he was expecting asking a reaper and and angel to work together would be difficult.

Likes

 * Thirteen prefers small dogs over large ones because she thinks they're cuter, as stated in the Devilgram Battle for the Bread!.
 * Thirteen has a sweet tooth, as seen in Lesson 72-7 when MC is able to convince Thirteen to answer some questions after she's given sweets made by Luke.

Story
Note: this section may include spoilers

Background
Thirteen has older sister named Candy. They seem not to get on well, as Thirteen told MC that if she told them too much, Candy would be upset and come for her.

Main Story and Events
In Lesson 38, "the reaper" became angry at Beelzebub for accidentally breaking Lucifer's cursed record "Hymn of the Reaper." In retaliation, she caused Beelzebub's life candle to burn significantly faster and almost extinguish.

According to Lord Diavolo in Lesson 65-6, reapers "don't fully 'belong' to any of the three worlds." This is why when looking to broaden the scope of RAD's exchange student program, Thirteen was chosen as one of the new exchange students.

In Lesson 70-16 Hard, Lord Diavolo offered to let Thirteen live in Purgatory Hall like Raphael, but Thirteen refused.

Relationships
Note: this section may include spoilers

Barbatos
In Nightbringer Lesson 15-1, Thirteen says she met Barbatos around the same time she met Solomon.

Solomon
In Nightbringer Lesson 11-8, Solomon mentions that he met Thirteen when he was a kid. It was in the middle of the night and she was dressed like a typical reaper, so her entire outfit was completely black. Solomon ended up screaming in terror when he saw her. He says that she told him that she wasn't his enemy, but her voice sounded terrifying to him.

In Nightbringer Lesson 11-10, Thirteen tells her side of the story of when she met Solomon. She says that she met Solomon back when he was still a regular human and she was still an apprentice reaper. Thirteen tagged along with her sister Candy to do some rounds in the human world that night. At that time, disease was running rampant in the human world and it was a reaper's job to harvest souls, so they were really busy. While her sister was taking care of some business, Thirteen decided to go for a walk. She wandered down some random back alley and saw Solomon through a window. The moment they made eye contact, Solomon let out a scream in terror. She then told him that she wasn't his enemy. Then, the moon came out from behind the clouds and lit up the alleyway. Thirteen saw the way Solomon's soul sparkled and she was captivated. Ever since, she's been looking forward to the day that Solomon's soul shows up on the reaper list.

Thirteen also mentions that the next time she saw him was when Barbatos suddenly showed up with Solomon at the Reaper's Cave. She says Solomon looked ragged like he was on the verge of death. Then, Barbatos told Solomon that he was the "Witty Sorcerer" and that he had to protect some kind of spring here inside the Reaper's Cave. For a while, Solomon stayed there and Barbatos would show up to take care of him. This only lasted until Solomon's wounds healed. Once he recovered, Solomon left without saying anything. The next time he showed up, he was the person he was today. However, she mentions that every since Solomon became the "Witty Sorcerer", his soul doesn't sparkle the same way that it used to.

Solomon once told Thirteen that he would allow her to harvest his soul if she managed to beat him at a game. One time, Thirteen stopped by Solomon's house while he was making dinner so he invited her to eat with him. Ever since eating his cooking, Thirteen has been particularly aggressive with Solomon. (Lesson 36-C)