A katauta is a traditional Japanese "half-poem," a short, unrhymed three-line verse often with a 5-7-7 syllable structure (or sometimes 5-7-5) used to express longing or questions to a lover, considered incomplete until paired with another to form a dialogue known as a sedoka (5-7-7 / 5-7-7), popular in ancient Japan.
Key Characteristics
Structure: Three lines, typically 5-7-7 syllables.
Theme: Often romantic, addressing a lover, asking a question, or expressing deep emotion.
"Half-Poem": A single katauta feels incomplete because it's a question or statement waiting for a response, notes
Britannica and Shadow Poetry.
Sedoka: Two katautas (5-7-7 / 5-7-7) form a complete dialogue or shared feeling, like a mirror of emotion.
Example (5-7-7)
Why do winter stars (5)
Shine brighter than summer stars (7)
As if they are shards of glass? (7)
Origin
Popular during Japan's Asuka and Nara periods (6th-8th centuries) as a form of intimate communication, says Sakuraco.
Source: Katauta Poetic Forms - Writer's Digest