Sometimes game could be bit boring when there is no event happpening(daily like 9 tails) and out of stamina.I know I know,what about areana right?.But, wouldn't it be nice if you could play already passed plot intances without any stamina and any rewards just to lessen the bordem?Games like cod have zombie mode for this exact reason(plus to practice skills). Allowing to replay already passed ultimate training is another option(it does really help to improve our battle skills too).