First, I like to check these gothic and lolita Japanese brand sites for inspiration. T-shirt reconstruction ideas are under the cutsew (or cutsaw, hah hah, Engrish) section, but everything is cute.
1 oversized t-shirt that you can cut down to baby-doll size
1 large white t-shirt for detachable sleeves (just the front or back will work)
thread, scissors, sewing machine, measuring tape, etc
1. Cut off the sleeves entirely and trim down the sides to a more fitted shape. For the pink shirt, I cut off the collar into a squarish neck, the black shirt doesn't need an altered collar. Save the sleeves for later.
2. Here I used another t-shirt for reference, marking out new armholes. These armholes must be shorter than the original sleeve's if you want them to be puffy, at least by an inch. Make sure they're not too small.
3. To make the puffy sleeves, gather the cut edges of the sleeves using a loose running stitch and pull the material together until it matches the length of your new armhole. Sew these sleeves to the shirt. For the best effect, gather up the top half of the sleeve, where it meets the shoulder, not the bottom half near the underarm.
4. Finish the sleeves by running elastic (the length around your arm) through the hem of the sleeve. I used thin elastic through the edge of the hem, where it is serged and this makes the ruffly bottom. For the black shirt, I cut open a little whole in the hem of the shirt on the outside and threaded thin ribbon into it, long enough to tie into a bow on the outside. This is helpful if you don't have elastic on hand, but the puff isn't as pronounced with ribbon.
5. Add lace and ribbons to your taste. I used cotton beading (or insert) lace on the shirt and cheap raschel lace for the sleeves and eyelet lace elsewhere. Sew up the sides of the shirt. Ta-dah.
1. If you have a square-neck shirt, sew two ribbons (about 10 inches) to the corners of the collar so that you can cross them around your neck and tie them in the back. This is directly from BtSSB.
2. You can make detachable sleeves out of more t-shirts. Just make a tube almost the length of your arm, add lace or ribbons and sew snaps/buttons that will attach to the inside of the t-shirt's sleeves. Another option is elastic garter around the top so that they can hold themselves up.
3. For the best results, sew ribbon horizontally across the front half of the shirt only. Because the shirt is slightly stretchy and the ribbons and lace aren't, if you sew ribbon all the way around, you probably won't be able to pull the shirt over your shoulders.
4. Don't be dumb like me and cut the back collar if you're also cutting the front. This made the shirt sag on my shoulders, no support.
That's all I can think of. I hope it helps and inspires everyone. I love to see more of these kind of shirts around! They're so cute. Also, I am perfectly fine with you copying my tutorial and selling your shirts on eBay, since I: 1) am already copying the design from a Japanese brand and 2) can't seem to make money no matter what I do anyways.