Add special ability (HP)????

[diamondx]

I just brought an item called special ability (hp). how do i use it to add to my unit. my rear/unit:

rear/elegahate +10
*tagami kazuchi soul
*stigma
*body
*stamina III
4 slots it has

now every time i goto to the grinding shop to try to add this ability it doesn't show up instead it wants units instead, what i am doing wrong, please help me. side note (the item called special abiltiy (hp) adds 45hp to the following stamina III so it will be like 95 hp total, that's what i thought . correct me if i am wrong.

[Sizustar]

You have to add it in with 1 or 2 other rear unit with 4s, and choose to use that item when adding in ability.

And this type of question should be asked in the quick question and answer thread.
http://www.pso-world.com/forums/showthread.php?t=213385&page=569