If its a Red Innocent with the star it still needs to be Ko'd Yellow first then fused. This means that the Innocent will not gain levels on the farm and must be removed by combining it with a higher level Yellow of the same type of Innocent without a star together. Or Red Innocents on items that have a yellow star on them already. Sometimes you find a Yellow Innocent on the farm with a star before Max level. Farmed Innocents are always born red unless you unlock a Innocent farm squad ability. You are then able to combine them or be bred in the farm. They can be moved from item to item but need to be ko'd in the item world to fully unlock them doubleing their level making them Yellow. They cannot be fused and have their stat bonus reduced. Red lnnocents are always hostile when first obtained. Or bred it he the Innocent shop, as you can see from the image combo innocents can be gotten by farming also. Yellow Innocents are ko'd Red Innocent and can be moved to and from items freely and fused with the same type.

Each weapon/item can have only 1 Unique on it at 1 time. Some are on weapons automatically and the rest are gained from defeating Item gods every lvl 100 in the item world. They can't be fused and can't be moved from item to item. Unique Innocents are always freindly and have 1 unique bonus only. 1-2 2-4 ect and sometimes you can talk to them on item worlds every 10 lvls once ko'd. They always have the words innocent over there heads in the item world. The Types of Innocents are Green Unique, Yellow subdued, and Red subdued.

And what type of innocent that appears on an item is random.

Innocents never appear on store items bought at the base, but do randomly show up on items in the item world shops every 10th lvl or on random item room shops. They appear randomly in items gained on maps, or ones stolen from enemies or can be farmed once tamed in the innocent shop. Innocents are monsters that power up your character stats that live in Disgaea 5 weapons and every other type of items even 1x use ones.

Disgaea 5 how to combine innocents