How did Greeks tell their narrative when telling the history of pederasty?

Pederasty would have been considered a normal practice within ancient Greek culture. There weren't really histories of pederasty as such, but rather pederasty was reflected in Greek art, theater, poetry, and history just as heterosexual practices are reflected in many aspects of modern European cultural productions. One underlying factor in the prevalence of pederasty was the extreme homosociality of Greek culture. In general, men socialized with men and women with women, and there was little opportunity for cross-gender social interaction, meaning that friendship and affection were almost exclusively focused on people of the same gender, with the exception of some female courtesans and entertainers participating in male social events.

The narrative of pederasty was intertwined with that of masculinity. First, we find a view that the older erômenos expressed masculinity by acting as the penetrator. In a variety of sexual activities, including oral and anal ones, intercourse with women, or the practice of an older male penetrating the closed thighs of a male youth (something frequently portrayed on pottery), penetrating was considered masculine and being penetrated effeminate or associated with youths who were not yet able to grow full beards, or had not fully transitioned through puberty to male adulthood. 

The association of pederasty with masculinity is emphasized in the accounts we find in Plato and Greek historians that associate pederasty with bravery. These accounts argue that lovers serving together in the army would be inspired to greater feats of bravery because they would wish to impress their lovers and also because they would be concerned with the safety of their lovers. The story of Socrates saving Alcibiades at the Battle of Potidaea is an example of this type of narrative.

Many poems speak of love of older men for young boys. In lyrical poetry, these can take the form of first person accounts praising the beauty of a youth and expressing longing for the youth. Theognis and the early symposiastic poets are examples of this sort of portrait, and Theocritus is an important Hellenistic source. Greek Old Comedy and satyr plays often make fun of old men who lust excessively after young boys. 

In Plato's Symposium, the character Aristophanes gives a humorous account of the history of human sexuality, but his speech about people having originally been two bodies stuck together is meant as funny (as one would expect from a leading comic playwright) rather than reflecting actual beliefs about the origin of human sexuality.