Well a single kiss ended up killing her, so either Zeref raped her corpse or she's a virgin.
Why? August has barely gotten any panel time since Larcade was introduced, as for actually knowing a counter, he can probably use the magic itself. The guys is said to know everything.
Sure, im not saying that Zeref isnt the strongest, he is. What i'm saying is that his immortality could be the key factor that establishes him as the strongest.
Sure, he could match Igneel powered Natsu, but i attribute that to his immortality, especially since IgNatsu without immortality was still on par.
When did Brandish mention Zeref's power? As i recall in 500 Brandish was just wanking the 12, not Zeref. Dont remember what Yajeel said, but like i said before, Zeref is still the strongest