The pants she's wearing are called monpe. I just made a pair yesterday in a day.
You can learn how to make them here, but this video is in Japanese. If you have basic sewing knowledge, you should be able to get it.
There is no pattern, only a cutting guide. 2 meters of fabric is able to do it perfectly with no fabric waste whatsoever.
Perfect for people who always feel like their clothes never fit! If you are concerned about the size, here are the pants on me (5', 90lbs) and my husband (6'1, don't know but he looks like fanart of Laios).
if you think you are bigger than my husband, all you have to do is scale the rectangles up so this measurement is 1/4 of your waist measurement.
But don't worry if it isn't perfect.
You can wear them as regular pants, or over kimono.
I want you to make these pants. Make monpe and experience the joys of adjustable clothing that will stay with you for years. Experience the joy of sewing something you know will fit and be well-made and usable, with no precise measurements besides hemming them to your height. Put on these pants and feel superior because you made something that the store could never give you.
Weight fluctuations? Pregnancy? Really thick kimono? Need to wear a lot of layers? No problem. Monpe will help you. Monpe will always be there for you. You can't get that at the mall with the rest of the slave labor clothes.