Ive tested lots of things methods ...this is the best way:

1: Locate Blade and Souls bin folder (mine was in C:\Program Files (x86)\NCSOFT\BnS\bin)

2: inside this bin folder, put the "bladeandsteam.cmd" file -downlaod here: https://drive.google.com/file/d/0B5JhV9Wrn-QfTnlSal82WXR2Mlk/view?usp=sharing

3: Now go to steam and add "Non-steam game", go to browse and locate the blade and soul "Client.exe" (its in that bin folder we were working in earlier)

4: once it is in your library, right click the new game entry you jsut made (it will be titled Client) and click properties

5: Rename it Blade & Soul

6 Click "set launch options"

7: paste this there:

/LaunchByLauncher /SessKey:"" /MacAddr:"" /UserNick:"" /CompanyID:"0" /ChannelGroupIndex:"-1" /ServerAddr:" " /StartGameID:"BNS" /RepositorySub:" " /GamePath:"" /LoginMode 2

8: GG