Knowing flacy is on the Green team, I'm asking on purpose! What do you think of Kushy?

To get straight to the point, I don't think it's really necessary. First off, my recommended Blue team composition is: Flo, Sivi, Evelyn, Fear, and Cole. If you were to include Kushy here, it would be a swap with Cole, but Kushy's shield references the caster's stats, so it inevitably costs resources. Also, while the drain debuff is strong, considering: Red → You can just overpower with raw damage, so drain's importance is low. Green → You recover through your own skills with healing/regen/pseudo-block, so you end up healing anyway. Blue & Yellow → You just need to tank with shields, so drain's importance is low. Sky → Basically similar to Red, the pillar's Rusa focuses on barriers. Nether → Primarily relies on Paratea's barriers. It seems difficult to get the full effect unless the battle drags on. And the Blue team's concept is more about short, decisive battles.....

By the way, I think it's a safe and strong choice to invest in cultivating Prima, Evelyn, and Cor, and then add Cor and Sivi who only have their signature weapons (ヾﾉ･∀･`)