"Be Mine" is the fortieth episode in the first season of Teen Titans Go! and the fortieth episode overall. It is also the second holiday episode in the season and the series. The episode first aired on February 12, 2014 and chronologically takes place after "Opposites" and "Birds".
Beast Boy helps Terra escape the dimension she was banished to and once again continues his romantic pursuit of her. But Terra only has revenge on her mind and plans to destroy all the Titans on Valentine’s Day.
A flashback details Raven's battle with Terra and her imprisonment in a dimension where the villainess swears revenge on the Titans and promises to crush Beast Boy. Six months later, Terra angrily screams as chili falls at her causing Cyborg, who had thrown the chili, to question the source of the scream. Raven reveals that she imprisoned Terra in the dimension the Titans use to throw away their trash and tells the robotic Titan not to tell Beast Boy. Later, Starfire enters the living room where the rest of the Titans are relaxing and exclaims her delight over Valentine's Day. She proposes a Valentine's Day dance to be held where the Titans will reveal their true feelings for one another.
Robin attempts to brush the subject but pleads for Starfire to be his valentine which she agrees to much to his delight. She remarks that all the Titans should have valentines as Cyborg proclaims he's found one in Jinx. Beast Boy attempts to ask Raven but she retches in disgust and teleports away. However, he doesn't take this as a no prompting Cyborg to state that the green Titan is unfortunate that the only girl who loved him is trapped at the bottom of their trash portal. Beast Boy deduces that the girl is Terra and smugly smiles as Cyborg remarks that he didn't share the information with him.
In the hallway, Beast Boy tells Raven that he's planning on throwing away rope and she opens up the portal for him. Throwing the rope inside, Beast Boy watches as Terra climbs out happily exclaiming her freedom. He asks her to be his valentine, but she begins to refuse before stopping herself and promising a surprise for Beast Boy. He attempts to kiss her, but she shoots a boulder that throws him out the tower. Robin, Cyborg, and Raven are relaxing on the couch when Starfire informs that a visitor has arrived for a Valentine's Day visit and introduces a baby she named Cupid. Robin calls the baby cute but he begins to shoot arrows at the Titan's head forcing him to flee with Starfire carrying Cupid in pursuit. Beast Boy informs Cyborg and Raven about Terra's return much to Raven's horror who decides to use her magic to keep an eye on her.
At a warehouse, Terra is using her powers to repeatedly slam a boulder against the doors when she is approached by Beast Boy who invites her to the Valentine's Day dance. Noticing that all the Titans will be gathered in one place for her revenge, Terra agrees to go and continues her attempt to destroy the doors. When Beast Boy asks what is she doing, Terra lies that she needs to obtain something from the warehouse for his surprise. He transforms into a snake and opens the door for her as she shoves him inside to enter. Robin is reading a magazine on the couch when Starfire enters, frightning him. However, Starfire reveals that she only wanted to exchange hearts filled with romantic sayings relieving Robin until Starfire hands him a still-beating heart.
Raven is eating cereal as Beast Boy brags about Terra's surprise. She tells him that Terra doesn't love him, but Beast Boy misinterprets this as jealously. As such, Raven shows him a projection of Terra through her magic where the villainess repeatedly exclaims her hatred for Beast Boy. Beast Boy wails as a result as Raven attempts to reassure him that nothing's wrong with him and blames Terra. The green Titan, however, exclaims that he's no good for Terra but Raven states that there's another girl out there for him, referring to herself much to his denial.
That night, Beat Box plays music for the Titans as Cyborg attempts to dance with Jinx but is electrocuted by Prison Guards who reveal that he's not allowed to talk to the prisoner. Starfire gives Robin a kiss on the cheek for his last Valentine's Day gift and announces that it's time to announce their feelings toward their valentines. She reveals to Robin that he is like a brother to her much to his disappointment. Cyborg tries to tell Jinx how he feels but is shocked once again. Beast Boy laments that he doesn't have a valentine as Raven attempts to share until she is interrupted by Terra.
Donning gadgets to amplify her powers, Terra reveals her plans to banish the Titans to the center of the earth. She unleashes a tremor that swallows the Titans except Beast Boy who cries over her hatred for him. The Titans escape and charge, but Terra successfully defeats Starfire, Robin, and Cyborg. Raven attempts to banish her, but is distracted by an arrow from Cupid and is crushed by a rock. Terra gloats about her victory as she heads to destroy Beast Boy and he decides to sing a love song to reveal how he feels about her. Terra becomes touched by the song as Raven watches the exchange in tears. Out of jealously, she destroys Terra's amplifiers. Angered, Terra summons a ledge and charges at Raven, but the Titan stops her with a demonic punch and she falls back into the dimension. Refusing to let her go, Beast Boy jumps in after her as Raven sorrowfully realizes that she never got the chance to tell Beast Boy her feelings.