Recently I posted kat-tun's performance on hey hey hey music champ, then I remembered I'd seen this photo.. and wondered at Koki's weird new taste in pet animals... well kappa in this instance... and his usual 'maji de' and 'this is awesome' expressions...
So just in case your fangirl radar/curiosity kicks in and you are wondering what is a kappa, here goes:
KAPPA = River Imp or Sprite or Monster
Origin = Japan (with Chinese & Hindu Antecedents)
Kappa also called Kawatarō 河太郎, or Kawako 河伯
or Kawaranbe 河ランベ or Gatarō がたろう or Enkō 猿猴.
One of Many Japanese Suijin 水神 (Water Kami, Water Deity, Water Spirit))
More detailed information can be found here
So take a read and get to know your Idol Koki :)
photo credit: loveorlike.tumblr