yes that's whats bugging me so Gama learned the 4th and the 5th and that means he is still hiding his skills :P
every Form ie: fire,water,lightning has forms
Gama Showed us 3 forms of lightning and
Shin showed us i think 2 forms and
Zenmaru 2 forms i think
I suppose I should clear this up since it's probably due to ambiguities in my translation...
First, the "FORMS" (型) of the Ogame School:
雷電型 - Raiden Kata - the "thunder and lighting" form
水龍型 - Mizuchi Kata - the "water" form
焔燃型 - Kagutsuchi Kata - the "fire" form
土公型 - Dokou Kata - the "earth" form
虚空型 - Oboro Kata - the "void" or "shadow" form (famous for the "shadow stitch" movement technique)
When Kashitarou is referring to a 6th form, he is referring to another FORM (型) like the ones listed above.
The individual techniques use the character "式" which I have translated as "mode" for lack of a better term. This includes shidensen, narukami, gurensen, gekirin, etc (what most people would refer to as techniques).
Hope this helps clear things up. Oh, and chapter 121 is up if you're interested. Thanks for reading.
