Main World.
Konoha, year eighteen, winter.
Toyotomi Clan Grounds, study.
Snow fell silently outside the window, and the snow on the window frame had grown a little thicker. The fire burned brightly, the occasional crackle of firewood sounding especially clear in the quiet room. Sakura Haruno sat cross-legged on the tatami, holding a cup of hot tea, her gaze resting on Toyotomi Yinglang as he leafed through documents across from her.
"Yinglang, there's something I've always wondered."
"Go ahead."
Toyotomi Yinglang did not even look up.
"Why are jinchūriki immune to genjutsu?"
Toyotomi Yinglang set down the documents, leaned back in his chair, and looked at her.
"Jinchūriki aren't immune to genjutsu."
Sakura Haruno frowned slightly.
"They aren't immune?"
"Right. They aren't." Toyotomi Yinglang nodded. "The reason jinchūriki are difficult to control with genjutsu is that their spiritual energy is 'human plus tailed beast.' An ordinary genjutsu ninja casting genjutsu on a jinchūriki is pretty much fighting two against one."
A flicker of understanding passed through Sakura Haruno's eyes.
"I get it! Jinchūriki aren't immune to genjutsu, only to genjutsu cast by people with weak spiritual energy."
"Exactly."
Toyotomi Yinglang picked up his teacup and took a sip.
"If the caster's spiritual energy is strong enough to suppress both the jinchūriki and the tailed beast, then the jinchūriki will fall under the genjutsu too."
Sakura Haruno nodded.
"Then... what else does spiritual energy affect?"
"The Shadow Clone Technique."
Sakura Haruno frowned slightly.
"Shadow clones?"
"Yes. Shadow clones." Toyotomi Yinglang set down his teacup. "Creating a large number of shadow clones takes chakra. And after a large number of shadow clones die, you need spiritual energy to keep the fatigue they send back from leaving you a wreck."
Sakura Haruno's pupils contracted slightly.
"Then the reason Naruto can create so many