
Conduit and Circlet give you enough wave clear and poke to play the first phase of the lane. Chalice and aegis will help you get through the early stages of the lane. First relic choice is honestly up to you though, I think aegis is the most likely pickup, but there will be some games where beads may feel better. Up to you. The flare ward is also my go-to, it gives you the most information out of the 3 wards for spotting junglers rotating towards your side of the map, rather than only spotting them once they arrive to the actual lane.
Because of Kuku's mana conversion to INT, his build doesn't require too much damage. The choice between Breastplate and Genji's order is based on the damage type you are playing against. After Rod, upgrading 2 relics has felt the best over other items, combat blink gives you a ton of safety AND engage potential to 1-shot backliners + timelock aegis lets you bait a ton in fights, regen up and reset CDs. The two upgraded relics also provide a % increase of all stats, so all that mana you've invested into is going to go up even more and add to your damage. Outside of these 6 items, I'll leave a few alternatives below, but this has felt the most consistent for sure.
If you feel like you're dealing enough damage for the game state, or you just need some extra survivability, effigy is a solid replacement. It almost acts as a second aegis by mitigating 50% of the damage you take whilst active. Ontop of this, the mana it provides gets convered into INT, so it still offers some damage.
Not something I'd recommend often, but Wish Granting Pearl does provide a ton of stats that aspect Kuku can utilise. A lot of raw INT, Mana and HP to round out a build if you're feeling experimental.
If you're not a fan of having too many relics to play around, gem of focus can fulfill a similar role to combat blink, the MS on the passive helps with chasing down enemies and adds a lot of safety as well.