hmmmm... after a closer look at the guns they seem to be in between the blades so X-form unlocks a special twin blade class. I'll say twin gunner which makes sense in a way.
Now as for his stage 3 class - Flicker That class really gives him the name terror of death as he gets a scythe and that he wanted to regain what he lost which in the 3rd vol will become a hindrance as Ovan and Boradux want him to become a PKK again so 1 he can kill Ovan like Ovan wants him too, and 2nd Boradux wants to kill him as he killed her and took her chances away from becoming an ultimate PK'er.
4th Stage - X-form
I guess you can say that this is the light side form of the flicker, and my guess are that Haseo must go through some harsh ordeal over his 3rd form and when the people turn on him. Wanting to find a way to change that he gains the X-form which will help end this war against the AIDA/Avatars started by the Lunar Tree.
(well at least thats what I think)