This achievement pretty much stacks with the "All Costumes Complete" achievement. Contrary to the achievement requirement above, actually you DON'T have to obtain all items at the Shop with all Roses and Lambdas. These are the only things you need to purchase(with all 50 characters) in order to get this achievement:
-All 17 Edit Costumes
-All 20 Swimsuits
-All 30 Artwork (costs 60,000RR)
-All 4 Others Items (costs 67,000RR)
Remember you only need to purchase all the Artwork and Others items once, it's all the Edit Costumes and Swimsuits you have to purchase 50 times. Purchase all of those items from the Shop with all 50 characters and this achievement will unlock right after the Costume Complete achievement. For some reason you will unlock both achievements individually rather than 2 for 350G possibly because this achievement is glitched or the requirements for it are misunderstood.