Broken sword is still alive probably

This is a baseless theory.

I think broken sword is probably the one who caused smile of heaven to turn hollow. He is the one who purposely led Nephis down this path.

I believe Nephis was always supposed to become Nephilim and strangely that might be the reason why smile of heaven is actually hollow.

Anvil, song and Asterion (his participation in the whole thing is bit cloudy for me) fought broken sword because they knew what he had done.

I believe broken sword is still alive and kicking and is probably sacred. Anvil and ki song tried to Assassinate Nephis plenty of times not because of their petty animosity with broken sword but because of what Nephis may become.

If broken sword's future plans require Nephis and her becoming a full fledged Nephilim, then anvil and ki song might have just wanted to prevent him achieving that goal.