WARNING: The following contains major spoilers for Black Widow #13, on sale now from Marvel Comics.
Natasha Romanoff's exploits as a spy, assassin and hero have defined her character since her first appearance. In that time, she has always given off the vibe that she has a situation under control and, even when she's beaten and bloodied, can still edge out a victory. That being said, there are times where even someone as skilled as the Black Widow must admit defeat or even feel fear. This is best exemplified in Black Widow #12 and 13 (by Kelly Thompson, Rafael T. Pimentel, Jordie Bellaire and Cory Petit) when she encounters the highly dangerous assassin known as the Living Blade.
In the 2020 series, Natasha Romanoff has endured heartbreaking losses after a collection of villains planted memories of a husband and son in her mind. Because the love is real, she decides to separate from them so that they can live a happy life. But following the feelings and experiences she felt with them, she decides to change her tactics from revenge to justice. As a result, she decides to claim San Francisco as her new home and city to defend. In doing so, she's made a small collection of heroic allies like Yelena Belova and Anya Corazon and encountered villains never seen before, including the Living Blade, who terrifies Natasha in a way that is new to readers and totally justified.
In the past, Natasha has faced alien threats, betrayed her friends, and was even killed by one of her allies. But no matter the situation, she's always faced it with stoicism, confidence and the inner motivation that she'd survive. But that has never meant that she doesn't feel fear. Instead, it implies that when the time comes where she's on the defensive, it's a situation that demands 100% attention and caution. The Living Blade shows this in an issue-long fight with Natasha in survival mode as his speed and ferocity get the best of her. However, when she reveals that she'd rather die than run, he leaves her with the promise of a reunion.
It's not like Natasha to live in fear, and because of this, she's lived life as if she's totally forgotten about the Living Blade. But in her line of work, it's also detrimental to her craft to live in fear of an enemy that's remained largely inactive. Whether or not she's forgotten about him isn't confirmed, but the sudden shock of seeing him again proves that she lulled herself into a false sense of security in his absence. But in her instant fear also shows that Natasha will have to face a choice that challenges everything she has taught herself since encountering him the first time.
When meeting the Living Blade again, she immediately remembers her past meeting and sees CLint in the other room, seemingly unconscious or worse. But instead of rushing in, she thinks, "...I can't do this again!" Not only is this out of character for Natasha, but it also means that she will have to decide whether she can handle facing him again to save her friend or try and escape him again. It's not like Natasha to feel this type of fear and clearly accesses a part of her mind that never trained for this. But even more interesting is how one man can evoke such a vulnerable side for her.
The new Black Widow series has seen Natasha pushed to her mental limits both emotionally and now physically. The Living Blade doesn't need a name because his presence is enough to cut to the core of anyone. For Natasha, her core is someone who isn't used to the natural fear she feels when facing a powerful foe. But by showing this vulnerable side allows the character to evolve in ways that haven't been seen, and by using her need to help others as motivation, she will finally have to face her fears.