Houka knew that Orochimaru had built many secret laboratories, but only after following Yakushi Kabuto and raiding them one by one did he realize just how many that mad research fanatic had actually built.
It took them nearly three months to completely clear out the vast majority of the laboratories.
Some of these secret laboratories were still in use, while others had already been abandoned. Yet even the abandoned ones contained plenty of valuable things.
Yakushi Kabuto took the best and discarded the rest, stripping Orochimaru's accumulated resources clean.
Meanwhile, Houka began guiding Uchiha Sasuke in his training. He started right away with the good stuff, teaching him Lightning Blade, the upgraded version of Chidori.
Compared to Chidori, which required charging up and could only attack in a straight line, Lightning Blade fully made up for those shortcomings. It was more powerful and far more versatile as well.
Uchiha Sasuke had exceptional talent in Lightning Release ninjutsu. In just two months, he had gotten the hang of Lightning Blade, after which Houka had him develop derivative versions of it.
Uchiha Sasuke was somewhat confused.
So Houka demonstrated Lightning Transmission, which Kakashi had derived from Lightning Blade, for him.
Lightning Transmission involved creating a Shadow Clone, then having both the original body and the clone use Lightning Blade at the same time. Through subtle coordination and balance, they formed an immensely destructive chain of lightning between the two Lightning Blades, sharp enough to sever even a Tailed Beast's tail!
Houka himself had silently trained with Shadow Clones for several years before mastering this technique. Who knew how much hardship he had endured?
When Uchiha Sasuke saw Lightning Transmission, it was as though the doors to a new world had opened before him. He immediately buried himself in training, ignoring everything else.