Here's the link :
https://tadoku.org/japanese/free-books/
https://www3.nhk.or.jp/news/easy/

https://kana-quiz.tofugu.com/
https://www.realkana.com/

Music used :
Society's Dream - Mini Vandals
Wunderkind - Freedom Trail Studios
New Morning - Track Tribe
Clean and Dance - An Jones
Rubix Cube - Audionautix