Participation is optional.

He chose to act on his own free will.

He is tackling his job with all his might and sincerity.

I am participating in the committee for the new project.

Mr. Ichii is my best friend.

He has perfectly mastered the Received Pronunciation of English.

I prefer tea over coffee.

He is bright, so he was able to solve the problem immediately.

It's better to go to bed early.

His opinion is insignificant.