What is the fine-grained topic of the following text: When it was announced last year that Captain Marvel would finally introduce the shapeshifting aliens the Skrulls into the MCU, fans were ecstatic, as it opened the doors for an adaptation of the Secret Invasion comic book storyline at some point in the future. Only return the topic.
Introduction of the Skrulls into the Marvel Cinematic Universe (MCU) through Captain Marvel.