You will need to get every swim suit in the game, except the ones gifted from Zack to other girls since they cannot be gifted. The hardest ones to gift are Christie;s swim suits. Keep trying to gift when your friendship is maxed and you should be able to gift one or two before they get refused. Use accessories and other items that she likes to build friendship faster.
Kasumi's CollectionAyane's CollectionHitomi's CollectionLeifang's CollectionKokoro's CollectionHelena's CollectionChristie's CollectionTina's CollectionLisa's Collection