Offerings (aka Spells) in Soul Sacrifice differ greatly either by element, type, area, damage, etc. All Offerings can be fused with copies of themselves to increase their quality (except Blood offerings). Each ☆ star increases the number of casts by one (1).
Fusing two of these (x2) ☆ offerings will result in a ☆☆ version, and two of these ☆☆ (x2) will give a higher 3 stars ☆☆☆ version. In total, you will need eight copies of an offering to fully upgrade it to 3 stars ☆☆☆.
Combining two ☆☆☆ "3 stars", however, will create a stronger version of the offering, if it exists. Most offerings have a (S) (M) (L) annotation to describe them: small, medium, large.
Soul Sacrifice attack offerings
|Blood· Homing · Throw · Beast · Special · Transform · Blitz · Weapon · Arm · Rising · Terrain · Bomb · Summon · Morph · Roar · Explosive · Mine|