Warning! Spoilers ahead for Supergirl: Woman of Tomorrow #1!
Supergirl and Superman are extremely powerful, especially under a yellow sun, but even with no powers, their confidence gives them a leg up over villains. In Supergirl: Woman of Tomorrow #1, Supergirl finds herself in the midst of a fight with her new ally's mortal enemy, Krem. This happens as Krem tracks down Ruthye, who has heard word about her trying to recruit bounty hunters to kill him.
The planet that Supergirl is on, orbits a red sun, meaning that she is powerless. Kryptonians always try and avoid red suns due to them feeling weak and drained. But in this case, Kara Zor-El travels there on purpose to exploit her weakness. Not only do Kryptonians' powers weaken, but their immunity to alcohol does too. Therefore, Supergirl is found at an alien bar celebrating her twenty-first birthday in style, by getting absolutely wasted.
In Supergirl: Woman of Tomorrow #1 by Tom King and Bilquis Evely, Supergirl's secret power is her confidence. Krem is a ruthless seasoned killer, he is almost unafraid of any threat. However, Supergirl makes him run for his life after Krem shoots Krypto with an arrow. Out of complete devastation, Supergirl charges at Krem and his ally. With extreme confidence, even with no powers, she grabs their weapons with her bare hands. Supergirl could've been seriously hurt, but the confidence that she exudes is enough to frighten the seasoned killer, forcing him to run for his life.
There's something remarkable about the strength that Supergirl exudes, even at her most vulnerable. Ruthye notes that Supergirl shows the confidence of someone that knows for a fact that their enemy can't hurt them. However, this would make sense on Earth as she has an incredible range of powers. But in this situation, she is just as mortal as anyone else. It's unsurprising that Krem ran as the sheer anger exuded from Supergirl's eyes is enough to make anyone fear her. This is something that Superman also possesses as he's often been able to defeat villains, even under a red sun.
The reason for Supergirl's sheer confidence is because of her time being a Kryptonian on Earth. Without her past experiences, Supergirl would just be as vulnerable as a normal human facing off against a deadly killer. It's likely that this has intimidated Lex Luthor in the past, as they have often fought off-world, under a red sun. Superman has a similar sense of confidence, even as his powers dwindle, which probably contributes to how much Lex hates him. Krem will continue to run in fear as Supergirl tracks him down, holding nothing back as she tries to avenge her fallen ally, Krypto. Supergirl: Woman of Tomorrow #1 is available in comic book stores and on digital platforms now.