His possessive case is very strong.

His name is used in the genitive case.

He used his knowledge as an instrumental case to solve the problem.

He made a sentence using the instrumental case.

He studied hard to pass the university entrance exam.

There is no vocative case in Japanese.

Kakuro is my best friend.

He passed the book to me.

This is an old Japanese textbook that explains the usage of '變格' in detail.

Gender identity refers to the gender that each individual recognizes themselves as.