The portrayal of Death as Grim Reaper often evokes him to be a male, at least in some countries. Since the original version of the comic is in German, and Death has a male grammatical gender there, it is not strange to imagine him as a man. Indeed, had my Death an audible voice, he would sound male. However, in Slavic or Romance countries, readers would be irritated that the girl identifies Death as a man, because in these languages, she has a female gender.
Fact is that in my story, Death has no sex or gender at all, because he is not a biological life form. He can change his appearance to whatever he desires, and the fact that at the moment, he has taken a more or less masculine appearance, has something to do with his personal development, but that's a story for another day.