Scarlet Widow

Scarlet Widow is the femslash ship between Natasha Romanoff and Wanda Maximoff from the Avengers fandom.

Canon
Avengers: Age of Ultron

Wanda took Natasha's jacket (revealed in a deleted scene). They fought alongside each other in the Battle of Sokovia. Natasha and Steve later began training the new Avenger recruits, including Wanda.

Captain America: Civil War

Natasha continued to train Wanda. The two took opposing sides over the Sokovia Accords and fought against each other at the Leipzig-Halle Airport.

Avengers: Infinity War

Wanda, Natasha, Steve, and Sam went on the run together, with Wanda occasionally leaving to meet up with Vision. After Wanda and Vision were ambushed by Proxima Midnight and Corvus Glaive, Natasha, Sam, and Steve showed up to save them. During the battle against Thanos' forces in Wakanda, Wanda leaped in to save Natasha and Okoye from Thanos' war machines. Natasha later returned the favor, teaming up with Okoye to distract Proxima Midnight from Wanda.

Natasha survived Thanos' snap to kill half the universe, while Wanda did not.

Fandom
AO3