You certainly don't need to be a Harry Potter fan in order to enjoy the Fantastic Beasts movies, but it definitely enhances the experience. Despite taking place before the events of the seven Potter books, the prequels are packed with enough Easter eggs and callbacks to choke a hippogriff.
We know that The Crimes of Grindelwald will introduce the human character of Nagini, who later becomes the snake/companion of Lord Voldemort. Today, we learned that the upcoming Wizarding World sequel will also feature a reference to Harry Potter and the Half-Blood Prince in the form of a character that's made an Unbreakable Vow.
The character is Yusuf Kama (William Nadylam), a French-African wizard tasked with tracking down the Obscurus, Credence Barebone (Ezra Miller). You can spot him attending the magical circus at 1:18 in the very first trailer for the fantasy film.
Yusuf's biography seems to indicate that his mother was raped by a dark wizard known as Corvus Lestrange, which resulted in the birth of Leta. It's not that hard to imagine, as the Lestrange family always put a lot of emphasis on the Dark Arts and became one of Voldemort's biggest supporters when he gained power.
A magical contract of sorts, an Unbreakable Vow means that a person is agreeing to fulfill a certain task or die trying. No joke, they legit die if they don't follow through on what they vowed to do.
We were first introduced to the concept in Half-Blood Prince, when Draco Malfoy's mother Narcissa convinces Severus Snape to do everything in his power to help her son in his mission to kill Albus Dumbledore. To seal the deal, he makes the Vow, with Narcissa's sister Bellatrix serving as their Bonder.
Ron Weasley was nearly tricked into making one by his brother, Fred, until their father discovered what they were up to. Fred received such a severe spanking from Arthur Weasley that he claimed his "left buttock" was never the same since.
Fantastic Beasts: The Crimes of Grindelwald arrives in theaters Nov. 16.