Serena first appeared in "Why Serena isn't in Alola", where she prepared to travel to the Alola region by plane. She is accompanied to the airport by Ash, Clemont and Bonnie who she says her goodbyes to. Before she made it down the escalator, she ran back up to kiss Ash. She made it down to her plane, looking back and blushing. Later, Ash and his friends are looking up at Serena's plane by the runway. In mid-air, the plane suddenly explodes, killing Serena. This caused Clemont to comment on how it was another Team Rocket terror attack and made Ash travel to Alola by train.
In "Time Flies", It is revealed in a flashback that Ash and Serena had a romantic interest in each other. One day, Serena indirectly criticizes Ash's last name. Ash turned aggressive, reminding Serena that he never made fun of her last name and asked what her last name was. Ash then compared her to Iris, Ash's travelling companion from Unova. Serena asked Ash who Iris was, this started another flashback.
In the short, "Serena cuts her hair", we see Serena get upset. For unknown reasons, she decides to shave off her hair. The next day, she is seen wearing a new outfit and without any hair (as well as a man's face pasted over hers and speaks in an electronic male voice). She shows her new style to Ash, Clemont and Bonnie. Ash approved while Clemont claimed "she looks like a man now".
Time Flies (Flashback)
- Serena was voiced by Lizzie Blinx, who also voices Mallow.
- In Episode 4, Serena was used in a gag which involved all of Ash's female travelling companions, this also includes Iris, Dawn and May, as well as May's Mom with the punchline being "...and that's why Misty's a virgin!"
- Serena has made the most appearances than the rest of Ash's former companions.