Perceptive little 'Nui.

Edit: For those who don't know, /anata/ is the basic 'you' pronoun* in Japanese. Using it this way is usually rude though, especially for strangers (you see it more often in anime though, along with /anta/ and the other 'you' words). You're generally supposed to use [NAME] + -san.

/Anata/, however, is also how Japanese wives call their husbands, so in this context it has meaning closer to 'dear', 'darling', 'honey', etc.

If both meanings are intended (like here, when Kasumi is being exasperated and rude while committing a Freudian slip), this can sort of be approximated in the translation by using 'dear' in a semi-exasperated/sarcastic tone, like I've done here.

(*Bear in mind that Japanese pronouns function more like nouns [in the sense that they are an open class and can be readily modified by relative clauses and adjectives] , and you would generally just drop the subject instead of it's understood instead of using a pronoun like in English.)

NNescio said:

If both meanings are intended (like here, when Kasumi is being exasperated and rude while committing a Freudian slip), this can sort of be approximated in the translation by using 'dear' in a semi-exasperated/sarcastic tone, like I've done here.

I don't think there's any Freudian slip here; she's probably using /anata/ simply because it's ruder and less respectful than the /shireikan/ alternative. She wants to treat him nicer, but not so nice that it contradicts her normal character entirely.

Don't have better idea to offer, but this sarcasm just feels off considering we have a younger girl calling an older guy 'dear' in a non-romantic manner.

Huh, didn't know you can use "anata" in an affectionate sense