Liezie

This was ons of my first ever mangas that i read. So my memory isnt that good about this manga.

I remember it is about a boy (black hair) and his mom said that he was a Demon baby or something at birth. I guess the dad said that he was a demon so the mom though the baby will also be a demon?. But one day the boy walked past or played near a pond and he fell in, and he transported to another world. And in this world he was a Demon king... or something. But he had someone, like a solder who kept him safe.. his name was something like David... but this 'David' tried to save the Demon boy and he lost his arm. And everyone thought 'David' died. But later on he came back alive and ofcourse, without his arm. There was also a blond boy that was friends with the 'Demon boy'. Thats all i can remember.
If anyone can help me find this manga I will appreciate it so much!

So I recall the two main leads was a tall, pretty boy with long hair and a short girl with short hair who is often mistaken for a kid because of how she looks and her height. The male lead may or may not be a prince. I don't remember. This takes place in a fictional world that is like Saiunkoku Monogatari. The story begin with the female lead going to pick medicinal plants or foraging for something. It begins to rain so she seeks shelter. There she stumbles on the male lead who is injured. She helps heal him and eventually he recovers. He leaves but returns later to repay her. I think. Skipping the middle because I can not remember anything. The ending was that the female lead was kind of forced to stay in another country or with a lady who have political power. I think she had political power. Basically she was forced to stay there to maintain the peace or something. After some time passes, the male lead and others goes to bring back the female lead. When they see her again, they see that she has grown taller and has grown some curves to her thin body. Her hair has grown longer and she looks more mature. She runs when she sees the male lead and he chases her. I forgot why she ran. He catches her and they talk and other things happen but basically, they get together and we have a happy ending. That's mostly all that I can remember. I think the female lead may have been learning about medicine, but I am not sure. Also, this manga I am searching for is not Kusuriya no Hitorigoto or the Apothecary Dairies. I do love that manga and anime too. I would greatly appreciate any help. Thank you.
Also, Saiunkoku Monogatari is a great manga and anime. I highly recommend the anime. I don't know why the manga is so short.