Running down the options once more:
[x] - Fuinjutsu:
[x] - Reverse-engineering the controllable, detonable shuriken.
We already have control over shuriken flight, and know how to make explosive tags. Both can be improved on, but it isn't a immediate concern.
[x] - Try to improve your basic chakra storage seal.
As we just saw, effectively doubling our reserves in a tight spot can make a huge difference. This is a priority to improve.
[x] - Ninjutsu
[x] - Learn more Fire Release Techniques
[x] - Learn more Wind Release Techniques
A few more jutsu over a week won't make a huge difference, especially since we'll have a jonin-sensei soon.
[x] - Genjutsu
[x] - Learn more wide area Genjutsu
We have other options for crowd control. We shouldn't let genjutsu fall by the wayside, but this isn't an immediate priority.
[x] - Kenjutsu
[x] - Work on your Iaido some more, and perfect your integration of it and your chakra flow.
This is critical. It needs to get done, the sooner the better - I was fully planning on sinking my next omake reward into Iaido.
[x] - Iryojutsu
[x] - Attempt to learn the Chakra Scalpel
We have a swanky chakra conductive sword as our main weapon, and a seal on our wrist filled with dozens of kunai as a holdout. Even if we learned it, it'd take significant effort to integrate it into our combat style.
[x] - Attempt to improve your Mystical Palm jutsu.
Right now, we can manage 5 seconds of Mystical Palm before running out of chakra, with full reserves. Since in most situations we need it, we
won't have full reserves, it's basically useless to us. Getting it running would both recoup our investment and make sure someone on our team can heal.
It'd also make a nice thematic counterpoint - after killing so many people, we learn how to heal. Creation to go with Destruction. Might help with the trauma having memories of that burned into your brain will bring.
I'm voting for:
[x] - Attempt to improve your Mystical Palm jutsu.
, but I won't be upset if working on our chakra seal or swordplay win - they're all viable things to focus on.