Things I think Haikyuu characters would do(anniversary addition) -
Tsukishima- he would record you at random (on dates, at hom, he'd take pictures too) and one day on your anniversary he'd set up a slide show to the song "To build a home" (The cinematic orchestra). He'd probably be a bit awkward about it, and be secretive, but it would have videos from even the start of your relationship. (He would do this maybe 4 or 5 years in)
Nishinoya- a dinner date at some fancy restaurant? Forget it, I see him taking you out in his car, windows down, late at night, driving around until he brings you to a spot where he had set up a picnic with whatever fast food restaurant (or whatever food) you like most!
Tanaka- again, I don't think he'd take you out on a dinner date, he'd probably spend all day out and about probably making you think he forgot, then he'd show up when the sun is almost set, as it's getting darker, get you in his car where he has an assortment of flowers waiting, a teddy bear (surprisingly big, he probably spent all this time getting it in the car) and other treats. You'd probably spend the whole night driving around to some music.
Tendou- oh Lords, get ready, this is chaotic, he'd take you out to some sort of amusement park, you'd go on various rides, probably through a haunted house (his personal favorite because you may cling to him) and then at sunset you'd end up on the Farris wheel, you'll probably be there going around over and over until it is dark and the lights come out. It'll bring a certain light to his eyes. Let's just say you may have a bunch of stuffed animals to bring home too XD
Lemme know if you want to hear more! And if you are a haikyuu fan check out my haikyuu comfort one shot book thing!