The supporting character's harem is very normal - Chapter 479 Pathogens

Time travel became a member of the Hakka family who beat the enemy. He is the twin brother of Yiermi, who is the odd one. He began to receive assassination training at the age of three, and began to perform missions at the age of six.

His hands were covered with blood, and his feet were full of bones. His legend began as a killer.

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This is an unremarkable hunter fanfic.

- Description from novelbuddy

An Individual from Earth finds themselves in the Shinobi World, equipped with a Scientific System. From that moment, he delved into scientific research far ahead of its time.

Zhou Heng drank too much wine, and woke up to find that he had time-traveled, and there was a beautiful woman lying beside him. Just when Zhou Heng, a bachelor of ten thousand years, wanted to take charge, he suddenly discovered that this woman who had a relationship with him was called Sadako, and she was the Sadako in Midnight Ring.

Sadako is just Sadako, pretty and human, but the memories that come out one after another make Zhou Heng discover that his name is Takeo Saeki, and he is the husband of Kayako in the Grudge of the Great Evil Spirit.

Later, at work, Zhou Heng discovered that his female colleague had a strange identity. The daughter of his client, Mimiko Mizunuma, had always been very interested in him when she came into contact with him.

- Description from novelbuddy