[be] two of a kind

(of people or things) to be the same in type or in character

The idiom "be two of a kind" originated from the concept of similarity or likeness between two individuals or things. It suggests that the two entities being referred to share similar qualities, characteristics, or behavior, making them comparable or alike in some significant aspect. The phrase exists to convey the idea of a unique bond or connection between the two entities, emphasizing their shared nature.

The siblings were two of a kind, often finishing each other's sentences and sharing similar interests.
Sarah and Emma are best friends who are two of a kind - they have the same sense of humor and enjoy the same hobbies.
The two politicians were known for their controversial statements and unconventional approaches; they were truly two of a kind.
Jack and Jill were notorious troublemakers in school; they were two of a kind when it came to mischief.
The artists had distinct styles, but they were two of a kind in their passion for pushing boundaries and challenging traditional norms.