Dr. Weissen is an inventor and researcher dedicated to studying Spirit Song mechanics and effects. His work focuses on Rin's unique ability to sing without losing her lifespan, observing how she feels rejuvenated instead of weakened, contrasting sharply with Finis's experiences. He developed echoing devices designed to amplify and store a Songstress's power while reducing the physical burden on the singer. When the military sought to weaponize this technology, Weissen refused. They seized his research, destroyed his laboratory, and killed his fellow inventors, plunging him into despair and crushing his hope. After Rin used the Song of Earth to restore his submerged laboratory, his motivation returned. He offered Al an apprenticeship, and Al became his student, assisting with inventions and research. Weissen's projects included a jet pack prototype fueled by his echoing devices; this technology later enabled Al to rescue Rin during a critical confrontation.