Best Worlds to Learn Fighting/Survival?

Which worlds do you know of that perks and regular jumper bullshit aside, are perfect either in terms of danger/action, experienced fighters, breadth of combat variety, etc. for taking an uchiha jumper gifted with internal energies (nen, chakra, street fighter ki, total concentration breathing), yet otherwise completely unskilled into a main character worthy combatant? (Or die trying)

Basically I want them to grow strong with what they have and can learn, not necessarily extra perks.

He does have slow passive regen that gets stronger the more he regenerates overall, and a slight increase to durability, but nothing more.

Preferably a verse comparable to or stronger than Naruto so that he doesn't outpace things too quickly, but not too massively above his ceiling.