Your teens may enjoy the embroidery services at Uniqlo. For your daughter, Ball&Chain bags are cute. I found mine at Shibuya Scramble mall, on the floor with handbags--the 5th floor, I think. I once found a location list, but can't find it now. They seem to be carried in some department stores, and appear to have pop shops they announce on their instagram. Your teens could probably track down locations quickly.
And if they're very high end, they might want to look for Japan exclusives from their favorite designers. My nephew bought a Japan exclusive at BAPE in Harajuku (a bathing ape) and another exclusive in London.
Really, clothes shopping may be a bit of a let-down. The nice stuff is expensive. They may find more enjoyment in buying accessories (bags, wallets, socks, etc.). Your daughter may want to watch some YouTube videos of what makeup/skincare to buy at DonQ.
https://www.instagram.com/ballandchain_official/