"Kelly's World" is the second segment of the sixty-third episode of Star vs. the Forces of Evil. It premiered on March 31, 2019 alongside "Out of Business", and is the second segment of the seventh episode in the fourth season.
Marco arrives in the Woolandia in search of Kelly's house after promising to make tortas with her. Her house, which is a giant pink hairy lump and later revealed to be her mother, is found and Marco is greeted by her dad who proceeds to attack him. Kelly comes out to tells him to stop as she was expecting him. Kelly is still bummed out from her recent break up with Tad, but she is not angry about leaving him. Instead, she is mad that he continues to call her out of the blue to tell her of his new enlightenment of "nesting", becoming a nest for birds. With her having to return a book to the library, Marco offers to go with her so that they can spend time together. She agrees and gives him a reddish Woolite wig for him to wear so that he can blend in with the rest of her world.
The two walk about and Marco learns that everything is conducted through fighting or physically harming one another instead of using money. ("My uncle bought a yacht once. He's still in the hospital.") They get on bus to the library, but when an elderly Woolite asks to fight for a seat, Marco offers it willingly, angering everyone on the bus. Kelly explains that not fighting is considered rude and everyone proceeds to get into fight with one another, forcing the two to get off early. Marco asks if Woolandia has any dojos. When Kelly cannot comprehend what that is, Marco reveals that it is for fighting. Kelly recognizes his karate moves as "wool-hair-do" moves and reveals that the book she is returning is about it. They bond over it for hours until Tad calls again. Marco tells her to just block him and they realize that it is 4:55; the library closes at 5:00.
Marco and Kelly run all the way to the library, but once they get their they are one second off and the book is considered late. The penalty for a late fee is to have one's hair shaved and Kelly resigns herself. Feeling bad, Marco offers to challenge the Librarian to a fight which she accepts. Marco and Kelly put up a good fight and they finish off the Librarian using the wool-hair-do moves that they learned; obliterating the Librarian into small Woolites. Kelly's phone rings again, revealing that she never blocked Tad. She admits that it is difficult for her to move on and Marco concurs as he still thinks about Star. They decide to become "break-up buddies" which includes hand holding hands and kissing on occasion and they leave the library hand in hand.
- Kelly's home dimension of Woolandia is shown for the first time.
- Since the events of "Conquer", Tad has achieved enlightenment by joining a self-help group, and he has become a "nester" (a living nest for mother birds).
- Marco previously believed Tad to have died in the battle against Meteora.
- Marco and Kelly calling each other amazing at the end of the library fight is similar to when Star and Marco first fought together in "Star Comes to Earth".
- Marco and Kelly reveal that they're developing feelings for each other.
- Marco reveals he doesn't know Spanish very well.
- Marco's line at the beginning of the episode, "That's one small step for Marco," is a reference to the famous quote by Neil Armstrong, "That's one small step for [a] man, one giant leap for mankind."
- Wool-hair-do may be a play on the Korean martial art of taekwondo. As a matter of fact, the symbols associated with it resemble Korean calligraphy.
- May 24, 2019 (Southeast Asia)