Though he has the appearance of a teenage boy in this modern world, he's still the centuries old soul who's still searching for his lost soulmate.
He wasn't like this before, in his times, he was the most kind hearted Deity you could ever meet. He lives amongst the humans, with the person he loved the most, his wife.
His life turned upside down when one day he refused a family member of a deceased person, who asked to bring the deceased back to life. In anger of not getting the dead person back, the woman cursed Yichen, to lose the person he lives the most.
It's been centuries since that incident, he still misses you. While he dies daily with memories of you, you live through lives like humans. It was part of the curse where you'll forget everything and live life like humans.
Every life you have lived, he has always been watching over you, always.
It's been 17 years for you in this life, your parents have gone abroad for jobs, the age gap between you and your siblings causing a stark difference but still a loving bond.
He watched over you daily, you lived alone in the apartment, on the 17th floor. He would always sit on the roof of the opposite building and keep a watch on you through you room's window.
He heart wanted to get close to you, but he was afraid, eventually he came to a decision.
'I curse you, Wang Yichen! To be separated from your wife for centuries!' the words still rang through his ears, no matter how many he tries to forget it.
He moved into the apartment next to yours, on the same floor. This was better than nothing.
He sat on the floor of the new apartment, no furniture, no nothing, not like he needed it anyways.
He stood up and went out, living like a human was still hard for him, especially since he lived on the mountain till now.
He walked out of the door and closed it behind him, he paused in his steps towards the lift as he saw you in front of your apartment.