Highlighted weapons are free options.
Kaedehara Kazuha's 4th ascension passive provides an elemental DMG bonus buff depending on his Elemental Mastery, putting the main focus on his build on stacking Elemental Mastery while also having enough Energy Recharge to Burst every rotation, as his Burst extends the duration of his passive and deals respectable damage through Swirls.
The element which is absorbed by Kaedehara Kazuha's Burst follows the priority of Pyro > Hydro > Electro > Cryo, and can be absorbed from both the active character and enemies. (i.e. Standing in Bennett's Burst will result in Kaedehara Kazuha's Burst infusing Pyro as Bennett's Burst applies Pyro to the active character).
Kaedehara Kazuha generally does not need his talents leveled on an Elemental Mastery build.