N.B. This is a guide to the original FFVII.
In Wall Market in Midgar, Cloud must dress up as a woman to gain access to Don Corneo's Mansion. By obtaining certain Key Items, it is possible to guarantee that Cloud will be chosen by Don Corneo; particularly useful as in more recent editions of the game, having Cloud selected counts as a trophy/achievement - "Consummate Cross-dresser".
When I say "best" or "most useful" here in reference to a Key Item, I mean best in terms of helping Cloud get selected by Don Corneo over Tifa or Aeris.
First, head right at the lowest part of the first screen to head to outside Honeybee Inn. A man there will say that Tifa is going to Don Corneo's Mansion. Then head all the way up until you reach Don Corneo's - after you talk to the bouncer, Aeris will insist on Cloud dressing up as a woman.
Go to the Clothes Shop. The woman there will say that her dad is fed up of working. Go to the bar and find her dad - Aeris will talk him into making a dress for Cloud.
Head back to the Clothes Shop and talk to people. When the clothes designer asks what you want the dress to be like, the best option is "something soft"..."that shimmers". This gets you Key Item "Silk Dress". The next best option is "something soft" "and shiny" (Key Item "Satin Dress"), the worst option is "something clean" (Key Item "Cotton Dress"). Aeris will mention a wig.
Save your game now. To get the wig, you will need to go to the gym. Here you will do squats - winning at squats earns you the best Key Item ("Blond Wig"), tying earns you Key Item "Dyed Wig", and losing earns you "Wig". Saving was important as you may want to load up again if you didn't earn the Blond Wig, and keep trying until you do win at squats.
Before heading back to the Clothes Shop to dress up, there are some more things you can do to make it more likely you'll be selected by Don Corneo.
First, head to the Diner. Sit down and pay 70 Gil for a meal - it makes no difference which meal you choose. Once you've finished the meal, you must say "It was alright" to get Key Item "Pharmacy Coupon".
Go to the Pharmacy. Here you can swap the Coupon for a medicine. The best one to get is "Digestive", then "Deodorant", then "Disinfectant". Head to the saloon (where the clothes designer was drinking). You can give the medicine to the woman who is sick in the lavatory. "Digestive" earns you "Sexy Cologne", "Deodorant" gets you "Flowery Cologne", and "Disinfectant" gets you "Cologne".
Now, visit the Materia Store. The owner will ask Cloud to sleep in the Hotel and check out the vending machine overnight. At the vending machine, 200 Gil gets you the best Key Item, 100 Gil gets you the 2nd best, and 50 Gil gets you the worst. Make sure you have enough Gil first! After sleeping, go back to the Materia Store. Depending on how much you spent, you will get Key Item "Diamond Tiara", "Ruby Tiara" or "Glass Tiara"
Finally, talk to the chubby guy who is wandering around near the Save Point. He will give you Key Item "Member's Card", which allows you to enter the Honeybee Inn. Select a room to stay in. If you stay in the "Group Room", you get Key Item "Bikini Briefs" by chatting the morning after. If you stay in "&$#% Room", you get "Lingerie" by talking the morning after. As far as I'm aware, "Lingerie" is slightly better? Furthermore, if you visit the central room the morning after before leaving, you can ask a Honeybee to put make-up on you.
Return to the Clothes Shop and get changed. If you have picked up all the inappropriate Key Items as well as putting on make-up, Don Corneo will select Cloud, over Tifa and/or Aeris, when visiting his "Mansion".
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Wall Market Cross-Dressing Guide
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Shinra Building Floor 63
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