what is a HM book?

[RotimiPika]

Like the title says what exactly is a HM book and how can I obtain it?

[Eckogen]

A Hongmoon Skill Book (HM Book) unlocks specific last tiers of a skill dependent upon which book you have obtained. These books only drop from BSH 4. They are a rare drop.

 

For example, if you go into the Comet Strike skill (KFM) the tier 5 skills all require an unlock. The first and third is unlocked via a skill book called Comet Strike - Volume 2, while the second and fourth are unlocked via achievement (Royal Zen Bean I believe)?

[RotimiPika]

oh thank you very much