Both Bai Yu and Zhu Yilong said in an interview that they improvised the scene in the taxi, when Shen is helping Zhao back home. It was not meant to play out like it did, with Bai leaning on Zhu's shoulder, but Bai could not help but tease Zhu and added that extra touch to the scene. Zhu played along and the result is for everyone to see.
Bai Yu ate a lot of lollipops for his role in the series, with the fruit flavor being his favorite. Bai Yu and Zhu Yilong stated in an interview that Zhu ate just as many lollipops as Bai during filming, and that he often stole lollipops from Bai as well.
Both Bai Yu and Zhu Yilong said in an interview that they read the BL novel the series is based on before they started shooting Guardian (2018), and they got some inspiration to their characters from it. However, they mostly just followed the script and based their interactions on that alone.
Lead actors Bai Yu and Zhu Yilong used their own voices for the parts that needed to be dubbed. All other actors had someone else dub their voices.
Zhu Yilong said in an interview he would have liked to have Black Cloaked Envoy's power (to learn) as his superpower. He said it was because he thinks BCE is the best "superhero."