Reincarnated in a depressing erotic world but living a normal life (right?)

Ever since Fionn understood the abnormality of his neighbors, which no one else seemed to notice, his mentality completely changed.

Due to the constant fear of living next to the unknown, he developed extreme distrust and suspicion towards others, creating all sorts of theories and conspiracies about any phenomenon, no matter how small.

And to try to understand what he didn't comprehend, he began to closely watch his neighbors from the shadows.

From these observations, he was able to understand to some extent how dangerous they were.

Starting with the mother and her vulgar behavior at home, after following her, he was unable to discover where she disappeared to or what she did at night to return with her clothes stained with a red liquid, but something told him it was better not to get involved any further.

"tch... Blood is hard to remove... Well, the brat will take care of it..."

The second was the expressionless maid with the most abnormal behavior in the family. 

She was the easiest to follow and observe. In one of his observations, he witnessed how a group of thugs who tried to hit on her forcefully were sent flying with a single blow while she continued with her usual shopping.

"Remember, Sara, when someone tries to attack you in any way, you just have to hit them!!"

"Yes, Sara will hit them."

And lastly, it was the new member of the family who seemed to have been recently adopted, being the one who seemed most normal. However, something normal surrounded by the abnormal felt strange in its own way, causing him to investigate her only to get a big scare when she smiled 'kindly' at him directly with eyes that clearly weren't smiling, causing his instincts to scream danger, thus stopping his observations of her.

"He's a smart boy, it would be a shame if 'something' happened to him for looking where he shouldn't."

After having watched all the female members of the neighbor's family, he finally decided to investigate the most suspicious of all, the youngest member, of a similar age to his, a boy named Mireya.

He was the most suspected of being responsible for everything strange with the other members. The maid only obeys his orders, the new woman is glued to him all the time and seems to have a clearly abnormal mother-son relationship based on what he has been able to see.

Added to that are things like him talking to himself all the time or controlling a mysterious group of small beings that roam the house, and it becomes impossible not to connect the dots to know who the mastermind behind all this is.

Under the premise that Mireya is responsible for all this, he decided to gather evidence by trying to watch him while noting everything he does in a diary.

And it was in this way that he noticed a mysterious flash of light coming from the neighbors' house. Deciding to investigate, he approached as close as he could to eavesdrop, only to discover a mysterious tall figure speaking some words in front of the mirror before disappearing.

After noting down those words as best he could, he tried to repeat them to understand their meaning.

"{Jiē kāi miànshā, zhǎnxiàn lìng yīmiàn de dàoyǐng}"

But to his misfortune, while he said these words, he was leaning on a 'reflective' window, thus fulfilling the necessary conditions.

"¡¿ehh...?! ¡¿What's happening?! ¡¡Mom, Dad, help!!"

Being thus absorbed into the other side of the veil.