As for the song Hanabi, you have to connect it to Hanabi~episode II~, because here is the lyrics towards the end of ~episode II~:
HANABI ~episode II~
The summer has come again and again since then
But why am I looking back upon the past again
Tracing the footprints?
I remember everything even now
Your voice calling my name, your casual habits
I want to forget, and I don't want to forget
Did I choose the right way?
But I keenly understand there is no answer
Whomever I may ask it to
Please tell me some day that you are happy
And smile
I gently lock the memories away
Leaving them to be beautiful
This feeling, this feeling, go up into the sky
And be dispersed beautifully like a firework
See, the lyrics is finished here and it does have to do with fireworks (last line). This is why Ayu named it Hanabi... at least, I think so.
