To use vimshell-kawaii.vim, you can change your VimShell's prompt dinamically by previous command's status code.
I reccomend to use NeoBundle.vim to manage Vim Plugins. If you are using NeoBundle.vim, you only need to write following lines to your .vimrc and just execute :NeoBundleInstall.
NeoBundle 'supermomonga/vimshell-kawaii', {'depends' : 'Shougo/vimshell'}
Run VimShell, and enjoy kawaii prompt.
:VimShell