Special site for 4
http://www.spyair.net/four/
Long digest clip for all songs in the album -
http://www.sonymusic.co.jp/player/HP080-01S
It's not in sequence , it's quite random all over the place
And I guess why they chose to include Imagination in 4 is to keep up with the 4 trend ?
4th album = 4 = 4 singles
In addition I'm・A・Believer has done very well & they probably want to capitalise Imagination in since both songs are used for Haikyuu :3