Shiro is a small, white, dog-like alien officially designated as Valkyrie's pet. Introduced without explicit backstory, he functions as a consistent companion. Valkyrie affectionately calls him "Spot" in English and "Shiro" in Japanese.

Beneath this pet persona lies a significant past: Shiro is secretly Spottenheim ("Shirokenhaimu" in Japanese), a veteran fighter pilot. This hidden identity surfaces when Mar, an alien affiliated with galactic pirates, recognizes Shiro and recalls his formidable reputation as a former comrade. Shiro consistently displays indifference to these acknowledgments, dismissing or ignoring references to his prior life.

In daily life, Shiro endures rough treatment from Valkyrie, particularly in her child form. She frequently pulls his ears, drags him around, or rides him like a steed. While Valkyrie frames these actions as playful, they cause Shiro visible discomfort or pain. This dynamic fuels recurring comedic scenarios.

Shiro's role remains static throughout the series, including its seasons, OVAs, and "Banquet of Time, Dreams, and Galaxies." He provides consistent lighthearted moments through his interactions and enduring physical comedy, with no substantial character evolution or new narrative developments specific to him documented.