Koi no gestalt houkai sounds pretty complex to me, it doesn't have a solo, but there are some pretty hard riffs, but I guess because the song is just really fast paced. The instrument breakdown part that comes right after the psychedelic sounding bridge (around 3:09)sounded pretty difficult to me. And like with QAT, haruna doesn't play the guitar for the live, but only for the last lead riff of the song(the outro). Which surprised me that Mami didn't do that part.
Metronome, the girls said it themselves that it's a hard song to play, mainly because there's a lot going on in each sec of the song. The solo itself isn't really hard to play, but the rest of the sounds pretty difficult, even though it may not actually be.
Scandal Nanka buttobase to me is under the same thing as Metronome, just a lot of riffs and tricks going on at 100mph. It sounds pretty hard to keep up within 3 minutes.
Want you solo has three different styles to it, and the lead part during the chorus must have been hard to play especially while singing back up, a lot of use of the Wah paddle.
Hoshi no furu, Anata ga mawaru, and Take Me Out solos sounds hard to keep up.
Basically majority of my faves songs solos seems hard to me. ^^
I'm not much of a guitarist so if anyone has tried this song's out or has the score of then can give me insight on the uses and difficulty of the song.