Worlds of Magic: Planar Conquest (JP)

Every unit is capable of receiving 5 spells cast on itself. Open your Spellbook, cast a spell, and then proceed the game turns until the spell is ready. Cast it on a specific unit. Repeat this 4 more times with 4 different spells (you cannot use the same spell multiple times as they do not stack).

The trophy will immediately unlock once the fifth spell has been cast on it. You can verify the number of active spells by selecting Armies Management and then selecting the specific unit. Move the right scroll button down to view the details of this unit. If it has any Spells there will be a section listing which ones they are. There should be 5 at the same time.