Haikyuu fell first / fell harder headcanons for ships that I personally like
Daisuga: Suga fell first, Daichi fell harder. Suga, essentially, developed a cute little school crush in their first year and sort of just nursed it quietly for a few years. Suga says hello to Daichi one day in third year, and Daichi decided he was going to marry him on the spot, and then realizes he has a crush on him.
Asanoya: Asahi fell first, Noya fell harder. Asahi fell in love steadily and in time with their growing friendship, Noya had once instance where Asahi laughed at a joke he made and was whipped from then on out.
Iwaoi: Oikawa fell first, Iwa fell harder. Oikawa doesn't remember a point in which he wasn't in love with Iwa - Iwaizumi crashes hard into an uncontrollable crush in their second year when Oikawa falls asleep on his shoulder on the bus.
Kuroken: Kenma fell first, Kuroo also fell first. These two drifted at almost the same pace, together, over a decade into a slow, steadfast love that cannot be shaken.
Bokuaka: Bokuto fell first, Akaashi fell first, too, and harder. These two were love at first sight. But Bokuto's first sight was "Oh... I think this boy is the one" and Akaashi's first sight was incoherent screaming.
Ushiten: Tendou fell first and harder, Ushijima caught up later. Tendou fell in love hard, within the first week they met, completely overwhelmed by him. Ushijima took years, to slowly settle into a friendship and then a love that he became incapable of living without.
Kagehina: They both fell hard and they both fell later. Kageyama was in love with him from almost the first moment they met but didn't even realize it. Hinata realizes the moment he gets on a plane to leave and can't turn around. They have to suffer through the "later" without each other until Hinata returns, but at least theyre the same level of absolutely whipped.
Tsukkiyama: Yamaguchi fell first, Tsukki fell harder. Yamaguchi falls in love with him quickly and happily, content to be his best friend and confidant in any capacity. Tsukki hits puberty and has to completely reorganize all his life goals to include marrying Yamaguchi as soon as possible.
Arankita: Aran fell first, Kita fell harder, but they both fell slowly. Aran knew he was in love after a couple years of being his friend and teammate and getting to know him. Kita fell much faster, towards graduation, when he was thinking about what his plan was and realized anything without Aran would be dissatisfying. Kita confessed within 24h of realizing this crush.