The latest episode of Supergirl, "Blood Memory," was a pretty overt rip-off of the Incredible Hulk. Supergirl season 4 has had a lot of twists and turns, with Kara forced to cut off her ties to the D.E.O. - and even have Alex's memories of her super-powered sister erased. Naturally, that put the two siblings at cross purposes.
"Blood Memory" is about the breakdown in the relationship between the two sisters, and how it reshapes them both as characters - particularly Alex. Through Kara, Alex encountered aliens at an early age, and learned not to fear the "Other." Without those memories, though, she has lost the compassion and empathy that defined her. This Supergirl episode was really a one-and-done to explore this disturbing new dynamic.
In a surprising twist, the entire A-plot of this week's Supergirl was basically a rip-off of the Incredible Hulk. It all kicked off on the other side of the globe, when the Russian Supergirl mysteriously collapsed, almost dying. Although the Russians were able to resuscitate her, the act led to a flare of unknown energy that swept across the globe to National City. There, the energy irradiated illicit drugs, turning them into something that mutated people into rampaging, savage, and angry Hulks. Although the makeup used for the furious drug addicts and frat boys looked different, Supergirl didn't even try to hide the rip-off. Dialogue confirmed that the pills had been saturated with Gamma radiation, and they swiftly became dubbed "rage." The only thing missing was a throwaway comment about how "the madder they get, the stronger they get."
It seems that, even in the Arrowverse, exposure to Gamma radiation can cause a person to mutate into a monstrous, rampaging brute. Of course, in Supergirl it didn't take long for the pills to fall into the hands of the Children of Liberty - a pretty convenient plot twist, given there was literally only one drug dealer in possession of a limited stock of these tablets. Amusingly enough, the Children of Liberty had no ethical issues consuming these drugs so they could direct their fury at a peaceful community where humans and aliens had coexisted for decades. It pretty much confirmed that, in Supergirl, the Children of Liberty are just thugs who hate aliens.
But why did the Russian Supergirl collapse, let alone generate a spontaneous flare of Gamma energy that had such a major impact on National City? That's unknown, but as the episode ended with the Russians deciding they had to call someone in the United States, presumably the Russian Supergirl plot - apparently inspired by the famous "Red Son" arc in the comics - is finally becoming important to Supergirl season 4.
Supergirl continues Sundays at 7pm on The CW.