There is a serial killer in my house!

A group of high-school students had an accident on their way to a trip and died but they find themselves in a classroom with a black sphere.

By day, Ha-Rin is a sculptor and teacher. By night, she turns into the serial killer Sow who, along with her protege Soon-Hee, uses a chat app to ensnare men with sex. After the deed is done, the men are kidnapped and tortured to death, punishment for being adulterers or for using women as if they're objects. But Detective Kim and his team are on these murderers' trails - will the duo's reign of terror be stopped?

Who do you think lives next door? A college student?
A secretary? A foodie? A quiet sort?
Or a killer?

Humanity's peaceful days all at once transform into an unspeakably odious hell.
The sudden invasion of wasp-like insects, along with gargantuan "dolls" wielding their enormous alien weapons, annihilating everyone in their path.
In the middle of the chaos, high school first-year, Iruma Ikaruga, fights to save his best friend and his beloved senpai from the dolls' assault with an unyielding spirit.
However, all that awaits him is despair.
Just what are the enormous puppets known as "Dolly"after?
What fate awaits Iruma?
The curtain has risen on humanity's "puppet show" of unimaginable despair, and the battle for survival has begun.

This manhua is a collection of short stories by this author. It is almost similar to the German Brothers Grimm's stories. However, these hold no morals but are more of a twisted outlook on life.

Plants have taken over the planet.
In 2017, the vegetation in Tokyo rose up and toppled human society in moments.
The few survivors are forced to live in the relative safety of a subway network, but supplies are running low.
Join an average high school student named Akira as he challenges the plants in a struggle for survival!

This world had rules. Rules that weren't meant to be broken. If only we had known those rules, everything could have been avoided...

From Hokutonogun.com and HappyScans:

A former professor of archaeology, Hieda Reijiro was expelled from the Japanese Archaeological Association for claiming that youkai exist. Ancient horrors come to life before our eyes as the youkai hunter wanders the land to find proof for his theory.

The included one-shot, "The Living City", won the seventh Tezuka Award in 1974.

A little girl that murders her abusive family, a doctor trapped in a plane with a violent infectious disease… These stories and more await you in the darkness of this collection of horror by Nori Ochazuke.

From asdf scans:
In near future, mankind has been defeated by the viral parasites named "Gastrea." They have been exiled into a small territory and live in despair, side by side with terror. In this world trapped in darkness Rentaro, a boy living near Tokyo and a member of the "Civil Security"—an organization specializing in fighting against the Gastrea—is used to accomplishing dangerous tasks. His partner is Enju, a precocious young girl. They fight using their peculiar powers until one day, they receive a special assignment from the government. This top secret mission is to prevent the destruction of Tokyo. Set in a near future, this thrilling heroic-action story starts now.

Fantasies inspired by reality. With a pen, I can make you laugh, cry or inspire you. Maybe. My misery will be your company.

From Jcafe24: Corpse Party: Blood Covered is about a group of high school friends in Kisaragi Academy. Kisaragi Academy was built on the grounds of Tenjin Elementary School, which was demolished after a string of disappearances and gruesome murders. After a mysterious earthquake, the students find themselves trapped in an alternate reality Tenjin Elementary School, where the murders of others trapped before them have continued unabated...

Alice Ryouhei will leave high school soon, but he's trying to avoid thinking about his future. Late one night, when he's hanging out with his tough friend Karube and his silly, girl-crazy friend Chota, they see fireworks. After one blindingly bright explosion, they find themselves waking up in a different world. In this 'Borderland,' people are forced to either participate in potentially deadly games or simply die. Will Chota, Karube, and Ryouhei be able to survive this dangerous new world, and is there a way they can get back to their original lives?

Fujisawa Ayana was horribly bullied at school. At first, she tried to defend herself, but she soon learned to just stay quiet and wait for the pain to end. However, the bullying escalated one day, when someone pushed her into traffic. At the hospital, as she recovered, she suddenly realized that even if she didn't fight back, her classmates were probably going to eventually kill her.

From this realization, she soon decided that the only path left was for her to take revenge. Her new plan included the students who bullied her, those who stood aside and laughed, and those who did nothing to make it stop. She began gathering notes on her classmates, planning exactly what she could do to make each of their lives collapse. While some of the students really seemed to deserve their fate, her plan also included classmates that she used to count as close friends...

A boy wakes up in a strange room and finds a girl passed out with him. They find out they both have weird collars on. The boy has a phone which seems to be connected to the people behind this. They want them to do what?

Adamsville” is an all ages graphic novel series about two middle school friends who must work together to solve a series of supernatural mysteries in their hometown. What they discover is a vast conspiracy that threatens to destroy everything they know about their lives, town and their future. Now they’re the only one’s who can stop the coming catastrophe.

The story centers around the film crew for Idol Survival, the internationally popular television program where swimsuited idols compete in games. The crew arrives on the same isolated South American island that TerraSave member Claire Redfield is visiting on an investigation.

A new transfer student has come into town, a girl with a mysterious air and black clothing who is called Inugami Sakuya. What few know is that by moonlight, she hunts and kills those possessed by "Inugami." A man can become possessed by being bitten, leading to a nighttime transformation into a beast driven to eat women. Sakuya gets no thanks for brutally ending the lives of these unfortunate men with her sword, and she is often too late to save the women they threaten. Sakuya also must deal with her own inner demons, which are all too real.