This probably wont work.

Cause the moment this is implemented, the next thing you see is Shisui Susanoo/Madara 10 tail/ Obito 10 tail/Pain 6 paths everywhere.

Most long time players probably have many of their basic or old ninjas of them.

Unless of course if the dev limits to what extend of the exchange is possible.

Which then defeat the purpose of having this exchange system.

But I agreed on changing 9tail naruto and Iruka for something else. Or change it to packs where we can exchange other similar worth ninjas.