A faint M UV = −14.5 Lyman-continuum leaker candidate in the epoch of reionization: Unprecedented Ly α properties at z = 5.725

We report the unprecedented Ly α properties of AMORE6, an extremely metal-poor (12 + log(O/H) < 6), low-mass ( M ★ = 4.4 × 10 5 M ⊙ ), and ultracompact (effective radius ∼30 pc) dwarf galaxy at z = 5.7253, which is gravitationally lensed by the cluster A2744. A prominent, narrow, and nearly symmetric Ly α emission line is detected at the systemic redshift (the latter traced by H β , from JWST/NIRCam slitless spectroscopy), with a rest-frame equivalent width of 150 ± 10 Å, a full width at half maximum of 58 ± 1 km s −1 , and a slight asymmetry, resulting in a flux excess of ∼10% in the red wing of the line. The negligible velocity offset from systemic (d v = 4 ± 67 km s −1 , 3 σ uncertainty), together with the sharpness and symmetry of the profile, indicates minimum radiative transfer effects, which implies a neutral hydrogen column density consistent with an optically thin medium that in turn is compatible with a nonzero ionizing photon escape fraction. If indirect spectral diagnostics calibrated at z < 4.5 remain the only viable tools for identifying LyC leakers during reionization, then based on its strongest indicator (Ly α ), AMORE6 stands out as one of the most compelling LyC-leaking candidates yet discovered in the epoch of reionization.