A genitive complement with a seeming tacit feminine noun

Question

In a novel written in English, police in a large city suspect a certain unkempt young man, the protagonist, of being a vagrant, and they have trouble with lots of those converging on that city. His respectable-looking acquaintance says he's a young friend of his from the country and he's become a bit confused, and assures the police officer: "I'll be responsible."

A translation into German that last sentence is as follows:

Ich nehme mich seiner schon an.

Among the various translations of the verb "annehmen" at dict(dot)leo(dot)org, one finds this:

sich[acc.] jmds. annehmen
to minister to someone

So "seiner" seems to be a possessive adjective qualifying an understood feminine singular noun in the genitive case. What would that feminine singular noun be?

And are there other verbs having genitive complements of this sort?

Answer 1

"Seiner" is simply the genitive case of "er". The fact that it looks like a possessive pronoun is irrelevant in this case.

(Diachronically there is probably a reason why a very rare form looks similar to another, more frequent form, but that doesn't affect how language works in the present.)

Answer 2

If the vagrant friend were female, the translation would be

Ich nehme mich ihrer an. (I will take care of her.)

There are many verbs with require the genitive, even though the number is decreasing, with the dative case often taking over. That is the "jmds." in the quoted dictionary entry => "sich jemandes annehmen", i.e. genitive.

It should also be noted that

I'll be responsible.

more directly translates to

Ich übernehme die Verantwortung. / Ich übernehme das. / Ich kümmere mich darum. / Ich nehme mich der Sache an. (take care of the case)