If you can type, this is ridiculously easy. If you can't, you have a week to learn. GO!
The Inner Ninja Challenge was a challenge for the game Typing Ninja Hunter that was released on July 10th, 2008 and lasted until July 17th, 2008. To complete it, the player had to score 25,000 points on the normal difficulty of survival mode. Completing the challenge would give the player the Replay 1 version of the Yoshiro card.