Why Did I Become A Trap In DxD?

So this is the first fanfic I'm doing, and I don't know when I'll post it yet ...... but it will be this week.

This fanfic is about a guy who died and was transported to the DxD universe as Astolfo(Fate).

Of all the weapons and powers Astolfo has, he will only have his spear (Trap of Argalia). With an increase in strength in your magic and physical abilities in general. His spear will be his sacred gear and his Rider form his balance braker, he would have to summon a griffin but I'm thinking about something else he can do in the future like transforming into a phoenix or griffin.

My main language is not English so expect spelling errors and I probably won't be posting very often, but at least one a week is my focus or even more