Please tell me the stem of this word.

This imperial rescript is a message conveying the emperor's will to the people.

This book contains a lot of rare words.

This book is difficult to understand because it contains many difficult words.

His rigid personality sometimes pushes people away.

He has a rigid personality.

He is good at learning foreign languages.

He was struggling to understand his internal language.

The Goto Islands are located in the southwestern part of Japan.

His palatial residence is built on top of a mountain.