You don't recall who you are, except for the name "Zero". You eventually come across a strange town and meet someone who is having trouble with a group seeking immortality. He grants you a home and in exchange, you must hunt down the people straying from the natural path. You also had a pen pal who sent you letters back and forth, and she invited you to finally meet her. Soon, the meeting happens, and becomes more eventful than you expected. However, once it was resolved, she decided to move in with you. Though her playful personality can be a lot at times, a strong bond begins to form.

Things have always been tricky with your family, and now, your parents are desperate for you to find someone worthy to marry into the family. However, you soon meet a pretty woman who is a powerful Demon Weapon. After your first fight, the two of you begin working together for a bit and then it transitions into something more. You're in love, and she loves you as well.

You were part of an experiment to achieve eternal life, but were freed by a sympathetic scientist. You began consuming blood from rotten people to appease your morals and eventually came across a rather intelligent woman. Soon, you discover she is an ageless witch and you begin to fall in love with her. When people begin to come after her, you vow to help her fight back, and she begins to reciprocate your feelings.

You had a rough incident with your parents, and both you and your sister were taken under the care of your uncle. Despite his quirks, he cared for you both and taught you how to fight. During his concert, you meet a girl who is quite childish. Soon you discover that she is partners with her sister and their "Meister". Your uncle then enrolls you and your sister in a special school, and you both begin to find yourselves in their presence more than you thought.

You grew up with your little brother and were forced to protect yourselves in the shady parts of your hometown. You both discover you have special powers and use them to survive. You then attract the attention of a special academy that offers the both of you a proper home and the two of you jump at the chance. Soon, you meet a pretty student who is a weapon belonging to a man obsessed with symmetry, but you begin to understand that she had a rough childhood as well. Soon, the two of you begin to develop something meaningful.

You've just enrolled in a school for students with special abilities. However, you don't have a "Demon Weapon" partner to work with. Luckily for you, a competent partner of a far less competent Meister agrees to partner with you. At first, you see this as just being allies, but soon you begin to see this as something more than that.

Y/N and his sister have had trouble with their parents divorcing and searching for new partners. They soon discover they have a special power and decide to bail. After ending up in a new town and new school for people like them, they begin hunting monsters for their eggs. On one of their missions, Y/N meets a Meister who is determined to be one of the best. Soon, he discovers she has parental issues as well and begins to bond with her. Two Meisters striving to reach the top.

You take on missions from an international organization hunting dangerous monsters. Then one day you meet a woman who is both playful and dangerous. At first things were just a game, but soon it becomes something serious. You've always been considered immature for being a hunter, but this girl has a better opinion of you.

You are a member of a secret organization hunting creatures from around the world. You are then transferred to a Cell in Japan and begin hunting curses there. You then meet a swordswoman who tries to hijack your mission and acquaint yourself with her. Maybe something more will come from this.

Y/N is a drifter hailing from a nation of endless winter. He took a job to go on an expedition to explore new land. He soon discovers a large island and large creatures that devour any human in sight. Along the way, he also meets a girl who spent her entire life inside a walled kingdom. After a few days, her nation eventually deals with the creatures and she becomes interested in seeing his homeland. He agrees to take her and brings her back. Soon, they begin spending time together and find similarities in their above average appetites. Soon, they become more than just friends.