The Signature Song

[TITANIC]

My friend asked me what is Ayu's signature song and I hardly tell him because she has got a lot of famous songs such as M, Dearest, SEASONS, and, Voyage not like other divas when you mention the name then you know their signature song. i.e Utada hikaru (First Love), BoA (Every heart), Namie Amuro (CAN YOU CELEBRATE?), Kumi (1000 no Kotoba) or Ayaka (Mikazuki).

So what do you think a song that deserve to be her signature song??