He is good at winning in mahjong.

He achieved a win in mahjong with astonishing skill.

He declared a win in mahjong.

He achieved a Tanyao (All Simples) in Mahjong.

In math class, we learned about the concept of union.

Kazumoto is my best friend.

Senwa is my best friend.

According to the traditional Japanese calendar, what is today's date?

Kazumiko is my best friend.

Kazutoshi is my best friend.