I would like to see, and i know of some players that have a similar idea to this, on your ninjas "Train" screen you can select the ninja, go on "Cultivation" tab and there would be a *on that if you press it you can pay, lets say 5-10 cuppons, and you would reset that ninja cultivations and give you the runes back.

The reason behind this, is that you have a limited amont of cultivation runes you can get dailly, and when you get new ninjas and want to get them on the team it gets really time consuming before you can get the ninja up and running, also with time you get better ninjas and the other ones just stay in the roster with unusable runes that will be wasted.

This would give a chance to run more diversed teams specially at higher levels where it takes over 15k runes to max a ninja cultivations.
Also it would help with Stong Approach and Ninja Exams for lower level players, since some of them need particular parties to control the fight, or a huge amont of battle power to push some of the exams.