Ryohei is my best friend.

He served in the military as a major.

He has morally degenerated.

This hardened dirt is so hard, nothing can be planted.

A central vowel refers to a vowel where the position of the tongue is in the middle.

The central vowels in Japanese are 'a', 'e', 'o'.

He is writing a thesis on the octovocalic theory.

It is said that this area used to be a mass grave.

I achieved a big success.

He graduated from the University of Tokyo.