I see no way to save this one without changing much of it.
Never write an unique. The ‘an with vowels and a with consonants’ rule applies only to vowels that are pronounced as vowels: you’d say an umbrella, but you’d say a unique umbrella.
I doubt the writer meant to say the character literally becomes the person whose clothes they wear. If the writer did mean that, the writer needs to think about it more until they realize this is nonsense. (Even if you have someone else’s appearance, personality, memories, etc., you’re not that person. You could have their exact genetic code, too, and still not be them.)
You have a unique ability. When wearing someone else’s clothes, you mimic that person’s appearance and personality perfectly. You collect personas by buying clothes in secondhand shops, but up until now, it was just a game for you. Then you find something very special.