Evolution of the luminosity of Hα (top panel), the Balmer decrement β (the intensity ratio between Hα and Hβ lines; middle panel), and the FWHM velocity obtained from Lorentzian fits to the Hα profile (bottom panel) in the spectra of AT 2021blu and AT 2021afy. The H line parameters inferred from the classification spectrum of Uno et al. (2021), available through the Weizmann Interactive Supernova Data Repository (WISeREP; Yaron & Gal-Yam 2012), are also included.