Kanna Skill Build

I'm confused about the additional effect on Retsu since GMS's description for quite a number of Kanna's skills are lacking...

The GMS description states it increases Shisen Gyouha's damage by x%, but then it also adds a passive +95%. Is the increasing variable supposed to be for the 3rd hit of Shisen Gyouha? And does it actually knockback because I can't seem to get it to proc.

It's basically what Link has said above this post. The Passive Buff is a buff to the base skill. Think Demon Slash Advancements. 1 Point gives the entire passive buff in one go. The skill itself, when active, gives a damage boost to the third hit (50% of the base damage added), and knockbacks. It only KBs on the third hit, and only the third hit gets the damage buff. So for example, if your hits with Gyouha do 100k damage normally, it will turn into 100k -> 100k -> 150k + KB.