Marvel's Natasha Romanoff's (Scarlett Johansson) backstory, showing the character once tried to assassinate Dreykov (Ray Winstone), the overseer of the Red Room. Unfortunately, Dreykov's young daughter was also apparently killed in the attack. For Black Widow, it was a sacrifice she was willing to make to kill Dreykov. It's only years later that Romanoff learns both Dreykov and his daughter survived the attempt. In fact, his daughter, played later by Olga Kurylenko, even becomes Taskmaster, one of the film's antagonists.
Marvel has subtly already teased its Blade reboot numerous times. In vampires as powerful MCU creatures, saying, "You know, we brought in Kree, Titans, vampires. Why is it the two orphan demigods are such a pain in the ass?" Another scene reveals the Time Variance Authority confiscated a cross, which may be one of Blade's weapons against the undead.
Like Loki, Black Widow also appears to have Blade connections. In Black Widow, Taskmaster is a character with photographic reflexes that can effectively mimic the fighting styles of almost anyone. The movie shows the character mimicking Black Widow herself, Captain America (Chris Evans), Hawkeye (Jeremy Renner), and even Winter Soldier (Sebastian Stan). However, one style may hint at a connection to Blade. Taskmaster often uses a sword in the film, which isn't necessarily a go-to skill of any of the Avengers she mimics. Because of that, the character may have learned it from the Daywalker himself.
Blade is an obvious choice to influence Taskmaster. In addition to being a half-vampire and half-human Daywalker, which gives Blade the powers of a vampire without the weaknesses, the character is skilled at sword-fighting in Marvel's comics. Blade uses several different bladed weapons in Marvel's stories, including long swords, katanas, and silver-based weapons. Basically, his name is Blade for a reason. Without a clear influence on where Taskmaster's sword skills come from, it's possible that the villain learned the ability from Blade. After all, Marvel has already teased Blade and vampires several other times in the MCU. With Marvel's Blade reboot on the way, more references to the Daywalker are inevitable.
There are other possible explanations for Taskmaster's sword, but nothing is a perfect fit. For instance, Hawkeye uses a Katana in Eternals, Taskmaster's skill could come from the character's comic book connection. However, that remains to be seen. With nothing being a clear influence on Taskmaster's sword, the explanation for the blade may fall to Blade.
