Well, attached is a save file which unlocks 98% of the costumes - I'm missing one or two, and I don't know which ones.
All the items that Etigoya mentioned have been done in the save file, and I'm not sure which two items remain.
The items found are (That aren't store purchased) are:
Ruby Brooch - Speak to the flower girl a lot
Bondage - Talk to the adult shop owner while wearing the vibrator
All rank up costumes at the bar
All event items - Photographer, Japanese Artist, Succubus, Vampire, Father's room
Not sure if you can access the forest up north, and if so, how to.
As for game endings discovered so far, I've found two which end the game.
Ending 1 - Buy the princess dress/wedding dress from the really expensive clothing shop, wear it, then go to the party (From the first screen after you leave home, talk to the two guards)
Ending 2 - Wear a perverted outfit and go to the party.
Speaking to the doctor at the clinic (first area) will eventually prompt you for a quest where you can talk to him about her father, and you have to save up 400k to get him treated for his disease.
Speaking to the guy at the bar (south area) will eventually prompt you for a quest to talk about her father, and save up to 150k. I think this one sends him off to a hospice or something.
Neither of the treatment options will end the game, but will let you access your father's room, which has an item hidden in it.
