The mental fatigue, that he started feeling from his training became a real issue as he reached a bottleneck.
The first thing he started doing was visiting the yamanaka flower shop a lot more frequently as he noticed that being there help with the restoration of mental energy.
He then started realising a series of test on the Shadow clone and Learning clone jutsu, he created a few clones and asked them to sleep, he knew clones could bring back senju chakra when dissipating so he was hopeful on finding an easy like hack that would let him gain quite a lot of time, but sadly this didn't work either so the only solution he had was to develop a Jutsu to help him solve the issue.
kayle started working on this project with all clones focusing and helping him as to solve this issue as fast as possible, the idea behind the jutsu he wants to create was a quite similar to the shadow clone jutsu, expect instead of transferring the chakra and experience he want to transfer the cumulative mental energy gained so he can use it like a baterie.
He slowly started experimenting, his knowledge about the cloning jutsu was extremely helpful as he already knew how it works, and after 2 months of hard work he finally had his first success.
He created a clone with very limited chakra and almost exhausted mental energy, having the clone rest made it restore its mental energy to around Kayle's full level of mental energy and once the clone dissipated it successfully transferred back this type of energy to it's owner.
After a few days experimenting with his new creation, Kayle noticed that the clone was extremely weak as it's sole purpose was to fix the mental fatigue issue, and it was very Inneficiant to be creating a clone that looked exactly like him for it to only be sleeping.
It took one more week to have the finished Jutsu after fixing these issues.
kayle: "Finally ! it's finished, good let's try it Lazy Cat jutsu"
A cat appeared out of thin air in front of him it looked around for a safe spot to laze around, it noticed a tree not to far away and easily climbed it and started taking a small nap after stretching.
kayle: "Haha ! finally! my master piece ! this is perfect now I can use the shadow learning jutsu to its maximum capacity without worrying about fainting out of tiredness... "
Maru that has been watching kayle all this time finally decided to comment on him.
Maru: "You do remember that you can't create more clones as you reached the limit of the shadow clone jutsu ? "
Kayle: "I know this already but this is an issue I would have to solve anyway, at least now I don't have to worry about that anymore... and all of can do is wait for my chakra reserve to be of the Jonin level and I will learn the multiple Shadow clone jutsu"
kayle sighted while looking at the cat sleeping lazily.
kayle: "Too bad I couldn't make it restore physical energy or I could train my body 24/7 , now even though I can survive without sleeping I still have to let my body relax by laying around, meditating or even sitting while providing him enough nutriments for its growth"
While kayle has been busy creating his new jutsu both Itachi and Shusui worked hard to establish a list of who they can save and who has to die inside of the Uchiha clan without creating any conflict for the future.