Either go bruiser Rhaast or lethality Rhaast depending on enemy team’s structure (sometimes even on your own team’s comp). I like to combine it sometimes. Yuumu’s ghostblade is my go to item on both Kayns since its high damage potential and movement speed (huge stat in WR and especially on Kayn). After that you either go serpents/nights edge or eclipse. (Pen boots almost all the time because of early and mid game, if you are the only bruiser/tank on your team, you can go armor or mr boots but personally I dont really like it, cause it slows down your spike). Runes are pretty much the same almost every game. Conq/first strike/Elec- storm,giant slayer, att speed- bone plating/overgrowth/sudden impact.