When it was first broadcast, "Rei I" scored a 7.2% rating of audience share on Japanese TV. The episode won popularity polls and was praised by critics, who appreciated the introduction of Rei's character and her mysteriousness. Scientific concepts are mentioned in the installment, which contains cultural references to DNA, nitrogenous bases and wave-particle duality. "Rei I" contains references to earlier fictional works as well, such as The Andromeda Strain and Sailor Moon. The laconic attitude of Rei's character has also been linked by critics to the Japanese socio-cultural situation, in particular with the generation born in the seventies and with a martyr complex. Critics analyzed Rei's home as well, comparing it to buildings of postwar Japan. Merchandise based on the episode has also been released by Gainax.
