Oooh, very good here! Very good! I don't think there are as many errors as Wildstorm-Of-Skyclan says.
"But why would Izuna want to approach the Spiritual Stones?" <-"Want to" makes it sound more serious. "Wanna" would be playful or joking around ^^
"A cave...?" <- The "a" makes it sound... I don't know. more correct in the ears of native speakers.
"To tell the truth, We - The keepers of the Spiritual Stones - should never let outsiders know the location of the Saintuary of the Stones. This is between you and me- okay? Don't tell anyone we were here."
"Alright." <-This would be better than "yeah", because "yeah" would make someone sound a little unsure as to what he is doing.
I agree with Wildstorm's last three suggestions.
"so, would you tell me HOW THE spirutial stones Are GOING TO MAKE MY WISH COME TRUE?". That sounds right.
wanna = want to approatch THE spirutal stones... A cave? to tell YOU the truth... never let outsiders know WHERE the sanctuary of the stones IS... between you and me THAT we're HERE NOW... so, would you tell me HOW THE spirutial stones Are GOING TO MAKE MY WISH COME TRUE? ...i'll tell you about IT when... STAY, I WONT BE LONG.(I guess, but I'm not sure it's what you meant...)