Headcanon: In contrast to Retsuko, Haida’s preferred music is 60′s-80′s classic rock. He has a collection of vintage and newly made vinyl records and spends time reciting the chords of his favorite songs on his own guitar.
When he discovered Retsuko’s death metal craze, Haida was awestricken by her. When they start dating, they both enjoy each other’s music, and share their personal favorites, even Retsuko’s more hardcore ones in terms of lyrics which make Haida low-key nervous.

