Chloe starts with the One Piece and Sexy bikinis. The Surfer bikini is unlocked on the PC store after playing with Amy at the sea. The Slutty/String bikini can be bought at the Red District store.
Chloe18: Back to Class is an adult simulation game where players manage the life of Chloe as she returns to school, balancing academic goals with social interactions and a "corruption" mechanic. "Extra Quality" in this context usually refers to community-provided walkthroughs that offer high-resolution guides, specific choice-consequence maps, or optimized routes to unlock all game scenes.