meaning of yuu-san

A girl called me yuu-san when she greeted me at messenger. I have a few knowledge about japanese but i didn't know this expression and she made it like it was a big secret. I don't why she doesn't want to tell me the origin of the name, either it is because it means something that she can't put in words or it's just a plain simple issue of handing me an expression i don't know and fooling around with that a bit.
However, i did try to look it up an neither dictionaries nor online search provided good enough clues. She did say she got the idea from an anime but it's not necessarily based on a character.
Anyway, can someone explain the possible meanings behind the expression yuu-san?

Let me know your actual name in refference, if you don't mind

My name is Ricardo, i'm a 28years old guy from Portugal, i don't see any connection there.

"yuu-san"
sorry, i don't have a sense,
probably she feels like something freindship with you

Thank you for your trouble. Yes, i figured that she likes me, i'm still not sure how much though. Anyone else want to make a suggestion to explain yuu-san? By the way, she likes the anime Fushigi Yuugi, the yuu in the title lifted a bit of a suspicion but i don't know the anime very well.

I just looked up the anime title, and the main character is named Miaka Yuuki (a girl) and there is a guy named Keisuki Yuuki (her elder brother, who is supposed to be a real nice guy).
So maybe, just maybe, the brother is called Yuu-san (shortened family name + "-san") by other female characters in the anime? I've never watched it, but just guessing from the name. Anyway, that is a friendly nickname. (The similarity between the word "Yuugi" in the title and the family name "Yuuki" is a coincidence I'd say. The kanji writing is completely different.)

it could be it. In that case i'll try to check that anime character. Thanks.

I am writing here again because i came to the conclusion that it was in fact intended to be "yuu-sama" instead of "yuu-san".

Googling after this expression, i found a few examples that didn't relate to persons. There is a japanese blog where a woman wrote a topic entitled "My yuu-sama" and in it there's the picture of a boy playing football. She then goes on to say that he is her yuu-sama, that likes him a lot and that he will be in J-league someday. However, the meaning still is shrouded, although from this blog i could take a wild guess and say it meant "idol".
But, that aside, "yuu-sama" is something that anyone knows bout and if so, will someone please explain the expression to me? Thanks in advance

it is "yon-sama", isnt it??

No, no, it's really yuu-sama. Does it say anything to anyone?

Normally people would make a nickname out of a part of someone's name, with "-san" (polite ending for names, like Ms. or Mr., which can be attached to either first or last name), or with "-sama" to be respectful or showing admiration. There are other endings that express more closeness as well.

So I imagine that the first part, "yuu" is just part of the child's name in the case of the Japanese blog, showing admiration on the part of the blogger.

Or maybe there is someone named Yuu that is supposed to be an idol that I don't know about :) but I am not aware of any... So, for the rest, I give up :)

Well, Yuu is the first name of the author of Fushigi Yugi... It's also the name of the male lead in Marmalade boy (by Wataru Yoshizumi)... Yuu as a name can mean tenderness/kindness, courage, or faint/dim... That's about all I can give you, though.

The suffix -san is usually tacked on to the end of a person's name (it's out of respect, I guess). If she doesn't know you very well, it doesn't surprise me that she wouldn't just call you by your first name, or a shortened version of your first name. People usually only call each other by their first name (without a suffix) when they're really close - like best friends, siblings, or significant others. I hope that helps! :)