Aiko is my favourite female singer. She's got a sunshine personality to match her cuteness! Also I love her voice and she's got a pretty unique style of song composing.
This is my fave song of hers called 'Ama no Gawa' / '天の川' meaning Milky Way (Celestial River):
'Eriashi' / 'えりあ し' :
Aiko being her exuberant self tossing plushies to her fans: