Issue with Sadaha Swordfighting

[RCadeGaming]

So, I got Sadaha Swordfighting a while back, and finally got around to learning the style. I've been specifically trying to learn the move "Buiji" which comes after "Haten".

It says to unlock the move "When Style is Fourth or higher, hit an enemy with a base move when HP is lower than 250". As I understand it, the Buiji move's base move is Haten, and I've landed Haten twice now with under 250 HP. I still haven't learned Buiji though. I'm wondering if this is a bug? Or have I misunderstood it?

EDIT: I know I can use a scroll. I just don't want to.