Serena/Relationship

Yuzu Hīragi
Serena initially paid Yuzu no heed despite their similar appearances (though she was a bit shocked at first). However, when Yuzu told her the truth about Academia's cruel and immoral actions against the entire Xyz Dimension, she began to gain worries about her words and cooperated with her to find the truth from Shun. When she learned Yuzu was missing after the invasion, she was filled with great grief since it was because of her the invasion started. Due to this, she was adamant about finding Yuzu along with Yūya while in the Synchro Dimension.

Yūya Sakaki
Although they haven't interact much in the series so far, Serena and Yūya often interacts in the Manzai episodes. In the Manzai episodes, both have a good friendly relationship overall despite having difficulty talking with each other at first due to their contrasting personalities, especially since Serena often rebuff any kind of jokes or anything that she deems pointless conversation due to her serious disposition. Nevertheless, Yūya continues to be kind to Serena, encouraging her when it was her time to Duel out of concern for her well being. Serena herself always siding with Yūya if Shingo bring up conversation that requires her to choose between one of them and she believes that he'll be able to convey his belief through the Entertainment Duelling that he inherited from his father. Her faith in him also caused her to be quite strict on Yūya, fiercely telling him to stop being too cheerful and focus on his Duel. When he first saw her, he mistook her for Yuzu due to their similar appearance. Yūya and Serena generally get along well, given their shared goal of rescuing Yuzu, but Serena's impatience and hot-headed nature tend to clash with Yūya's more patient and cautious nature. Despite that, Yūya does value her as an ally and cares for her well-being, as he refused Sora's offer to trade her in exchange for Yuzu's safety from Academia, saying he couldn't abandon Serena.

Serena's Duel with Yūgo, made her understand Yūya's intention of trying to make people smile through Dueling.

Yūgo
Serena initially respected Yūgo for the skill he displayed in his Duel with Shingo Sawatari, but changed her opinion upon meeting him. She was annoyed by Yūgo's attempts to hug her for mistaking her for Rin and derided his more spontaneous Dueling style compared to her own. Serena later changed her assessment of Yūgo during their Duel, and they parted friends afterwards. Serena was surprised to notice Yūgo's resemblance to Yūya, but she kept this surprise to herself.