This is a customized version of the NISSE firmware from Esrille Inc.
See my blog posts for how it has been customized (in Japanese):
http://d.hatena.ne.jp/mobitan/searchdiary?word=%2A%5B%A5%AD%A1%BC%A5%DC%A1%BC%A5%C9%5D

I (mobitan) do not claim any copyright for my modifications.
The same license as the original work applies to this customized version.

The original README follows:
--------------------------------------------------------------------------------
The Esrille New Keyboard - NISSE
Copyright 2013-2017 Esrille Inc.

This product includes the design and the firmware of the Esrille New Keyboard
being developed at Esrille Inc. (http://www.esrille.com/keyboard/).

See the file NOTICE for copying permission.