Yes, juban. Yukata (cotton summer kimono) can be worn with or without juban, and going without it is more casual. The juban's purpose to protect the kimono from your skin oils and sweat. They must be worn with lined kimono, which are more expensive.
What can I do if my Yakata is too long? Can I fold the cloth around the waist up and tie the Koshihomo to fix it? Or should i cut the end ... I don't want to do that :( ヤカタが長すぎるとどうすればいいですか？ウエストの周りの布を折り畳み、それを固定するためにコシホモを結ぶことはできますか？または、私は最後をカットする必要があります...私はそれをしたくない
You can use a second koshihimo to secure the fold under the obi. Look up how women wear yukata for reference on how to adjust the length and secure the fold.
Whenever I'm at a Ryokan, I honestly just tie mine as close to this as possible (which never comes out right) and I hide it behind my back lol. A lot of younger Japanese people don't know how to tie these either so I'm sure it's fine if you give it your best effort
Yukata are extremely informal and usually worn at hot springs, so these are not usually worn with Hakama. A Hakama is worn with a more traditional kimono which is usually made from different materials, and they also require a juban (an undergarment). Adding haori with hakama makes it the most formal looking.
