'~이' is a particle you can put after adjectives to make it a noun and the noun signifies 'a person who contains the outstanding characteristic of the adjective, inside him or her'
귀여운 = cute -> 귀염이 = A person who is so cute / 못난 = ugly -> 못난이 = A person who is ugly,
똑똑한 = smart -> 똑똑이 = A smart guy or girl, and so on
상큼한 = fresh -> 상큼이 = A fresh person
(Being fresh doesn't mean literally fresh in terms of expiration date or so. It rather means a person is pure, young, cheer and attractive rather than overshadowed by conventional bullshits or depression)
Please note that not all adjectives can make ~이