According to the records, the Sage Art used by Hashirama Senju originated from himself; it was not the Sage Art of Shikkotsu Forest.
In fact, Shikkotsu Forest did not possess Sage Art in the traditional sense.
Because there was only one slug in Shikkotsu Forest, and other living beings were rarely seen there, there was no need to develop a specialized Sage Mode for them.
As for the way Katsuyu herself wielded Natural Energy...
Katsuyu could teach it to ninja, but unfortunately, no one could withstand that Natural Energy saturated with a corrosive aura.
"Tsunade, have you ever asked Sage Katsuyu why, as a slug, she was called Katsuyu?"
"If it was a name, Katsuyu and slug sounded far too similar. But if it was merely a form of address, why not just call her Slug?"
Before signing the summoning contract of Shikkotsu Forest, Uchiha Ensei voiced his doubts to Tsunade.
"Of course it's because my name has always been Katsuyu!"
A gentle female voice rang out. A slug crawled over Tsunade's shoulder and answered Uchiha Ensei's question.
"Wow, what powerful energy!!!"
Just as Uchiha Ensei was about to say something, Katsuyu let out a shriek. Then seven or eight more appeared, crawling toward the two cultivation tanks beside Uchiha Ensei.
"Huh, there are still people with several bodies these days? I thought your kind had gone extinct. It really has been a long time."
Katsuyu spoke with some emotion, yet her casual tone seemed to reveal quite a few astonishing things.
"Katsuyu, can you tell me about things from a long time ago? Preferably about Goddess Kaguya, and someone named Xuanci... no, Jigen."
After signing his name on the summoning scroll, Uchiha Ensei sensed the contract connecting him to Katsuyu.
"Xuanci... I don't know that person."
"As for Kaguya...