I wish Ayu hadn't strained her voice so much
But it definitely resulted in some interesting songs, like Startin' and the GUILTY songs. This is how I've noticed her voice change:
1. poker face - WHATEVER
2. LOVE ~Destiny~ - evolution
3. NEVER EVER - Voyage
4. H - Bold & Delicious/Pride
5. (miss)understood - Secret
6. talkin' 2 myself - present