Jiraiya and the others did not really understand Kazemori Masaki's wishes for them. After all, they had no way of knowing what kind of people they would become. Still, those wishes were well meant, so they all accepted them without quite understanding.
Then Kazemori Masaki looked over the three of them and said, "You've had enough rest. Let's start training."
The three promptly answered and focused on the training ahead. Kazemori Masaki's exhaustive analysis had made them aware of mistakes in their past battles, and now they had a chance to try to correct them.
Training with Jiraiya and the others did not require great strength. Rather, he needed to reduce his strength considerably to help them grow. Otherwise, it would simply be an expert bullying the weak, with no value whatsoever. What Kazemori Masaki primarily wanted to pass on was experience, not anything else.
Thanks to his sage realm, Kazemori Masaki had excellent control over his strength, but he still needed to reduce it further. He therefore left a Shadow Clone to help them train while he went to check on Hatake Sakumo and the others.
Like Kazemori Masaki, Hatake Sakumo and the others fought in a direct manner. Only Heizo Hattori incorporated some variations into his fighting style. In Kazemori Masaki's view, the Hattori family's traditional assassination methods were already formidable. Their only problem was that they were of little use in a head-on battle.
The solution Kazemori Masaki later devised was to have Heizo Hattori learn to use misdirection with consummate skill, creating opportunities for assassination even in a head-on battle so that the Hattori family's traditional methods could come into play.
Heizo Hattori had used this approach in his fight with Jiraiya. But Jiraiya was too weak, and Heizo Hattori had not taken it very seriously.