There is far more group songs than solo's.. but again.. there is more of a good amount of solo song's than Yuki Sakakihara. ;A;
About... 4 different characters that have solo's... 'v'

With Yuki Sakakihara.. its just more or less one.. even then i would not count them as solo.. ah no wait... 2... but i can't listen to the proper version of it.. (its blanked out for me on Spotify.. and the youtube version is a live.. like i said before..)