This app can be used to learn finger spelling, which is a system for hand-expressing katakana in Japanese sign language. This is the premium version. There are no ads in this version.
You can find the free version here: https://play.google.com/store/apps/details?id=com.yubimoji

Learn yubimoji! The Japanese fingerspelling alphabet can be used to represent both hiragana and katakana. This is the premium version, which has no ads. You can find the free version at the link above.