(It seems that) She's not quite ready to take (drink) it black.

People who have followed this series may remember that little KC Kaga isn't the first shipgirl who Taisa has had asking Bismarck for black coffee only to find out how bitter it is. That would be Amagi-chan in post #5556416 (later revisited in post #6271145, which also incorporates post #5079833).

Welp, time to make Mocha as that's the only way to dilute the thing, Bismarck.

ezekill said:

Welp, time to make a mocha as that's the only way to dilute the thing, Bismarck.

And make sure Mainz either understands or is looking the other way.