Can someone recommend some vf fanfics? I've never read fanfics of manga characters before ...

There's so much, it's hard to say what will appeal to each reader. Here's a link to stories on AO3 sorted by the number of kudos they received, kind of a best of ranking:

http://archiveofourown.org/works?utf8=%E2%9C%93&commit=Sort+and+Filter&work_search%5Bsort_column%5D=kudos_count&work_search%5Bother_tag_names%5D=&work_search%5Bquery%5D=&work_search%5Blanguage_id%5D=&work_search%5Bcomplete%5D=0&tag_id=Finder+no+Hyouteki+%7C+Finder+Series

Thank you so much!

Obsession (is good )
National Pastime (is good)

i hope you will read this fanfic. it's really good.
https://www.fanfiction.net/s/9213629/1/Business-as-usual

Green_Destiny's fic Divining Infinity is outstanding and has the most beautiful artwork. You should check it out. http://archiveofourown.org/works/3706031/chapters/8202075

Thank you all so much for the recommendations! These will definitely keep me busy!

Eprime and ptw30 on livejournal have written really good ones

If you find something really good, I hope you'll come back and share the link with us. Don't let the self-appointed gatekeepers scare you off.

TBH, I'd just go to AO3, search for Finder series, and sort by kudos and complete works like so:

http://archiveofourown.org/works?utf8=%E2%9C%93&commit=Sort+and+Filter&work_search%5Bsort_column%5D=kudos_count&work_search%5Bother_tag_names%5D=&work_search%5Bquery%5D=&work_search%5Blanguage_id%5D=&work_search%5Bcomplete%5D=0&work_search%5Bcomplete%5D=1&tag_id=Finder+no+Hyouteki+%7C+Finder+Series

Kudos is a very blunt tool - it will show you what is popular, which isn't the same as good - but once you find an author you like and a style you like, you can go from there and look at similar tags and bookmarks by those authors. If you haven't read fanfic before, and don't know what you like then it's probably not worth trying to rec you something, because you don't know what you're looking for yet.

Thank you very much! I'll check them out :)

Will do!

Thank you lots! I wasn't too familiar with AO3 a few days ago. Still not as I just got my invitation to register the other day but I'm sure I will get the hang of it when I know how to use all of the functions soon.

Ah, didn't mean to put the other day but yesterday haha.

You don't need to register to use it, only to post content.

Does anyone have the fanfic Finder no Hyouteki National Pastime? It was taken down and I cant find it anywhere.

Wow you weren't kidding, this is pro level stuff (I didn't actually read it, only looked at the pics)
I especially love the way Aki is drawn, he can look like a guy, who knew