"Haruna doesn't know what this practice is for anymore!" Don't worry, Haruna, I suspect the same thing happens to admirals all the time. "Well, we've scheduled the maneuvers, we might as well do them."
Also, i think this joint practice is to get Katsuragi integrated with the rest of the exile Abyssal fleet as their second carrier.
Sshrssh
You look so cool, Raggy! Hoppo's happy to see your launching ceremony!
Hoppo Oneecha'!Lookiiit!
Plash
The ones teaching her are her fellow carriers, Houshou-san and Wo-Class-chan! Hoppo-chan will cheer her on, and Seaport-san will supply her!I-Class, Ro-Class, Ha-Class, and Ni-Class-chan will be the escort vessels deployed ahead of Katsuragi-chan!
Haruna doesn't know what this practice is for any more!
Nagato-san, Kongou-Oneechan and Haruna will be Katsuragi-chan's practice attack target ships!