Note: this app has own dictionary for Japanese language that need about 60 MB (and need Japanese font in your device).
I can't owe you this large byte size, but if you don't care down load size or interested in this functions, I'm glad, read follow.

This application can perform Japanese Kanji conversion using Mozc dictionary. As you can convert Kanji to Kana by selecting characters, it is useful for creating sentences and checking Kana reading.

The keyboard of this app is large and easy to press.
You can customize this buttons, colors and transparency.

If you're looking for a text editor other than an existing app, try this app as well.
The operation unique to this application, such as expansion of characters with swipe, clipboard management, join and divide pages, may make editing work comfortable.

About app permissions:
This app requires file (storage) write permission, but if you don't use file output, you can turn it off.
(If you use only Google Drive or clipboard, file output may not be necessary)

After purchase some features will be unlocked such as keyboard select.

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Another app "RK note" is for making short notes, and this "R-Kana note" is for making long sentences.
Anyway, I hope those will make you a little more comfortable and fun.