........I guess a lot of the bosses Dante faces were resurrected demons that his father fought long ago like lets say Trismagia or Furiataurus.
Funny idea for the Trismagia boss scenario when Dante faces him Trismagia since he is the all knowing oracle of the underworld he should speak in a whimsical, poetic, and riddle-like tone(most like a reference to the Divine Comedy since he was based off of Satan from the Divine Comedy) in an attempt to make Dante question his actions but Dante gives him an answer that was rather similar to Sparda's answer when Trismagia questioned his actions to protect mankind. In the end Trismagia dies but upon his death still questions Sparda's answer and only fought Dante to see if he could and felt rather upset or sad despite being the all knowing oracle still could never figure out Sparda's actions himself. Dante sees this and reflects on his past battles with Trismagia, Bolverk, and his past demons he realizes that demons and humans aren't so different after all. They all have one thing in common.........pride. Then Dante finally comes to a conclusion as to why Sparda decided to betray his demon brethren and side with the humans....well his own conclusion(which will be unknown to the audience).
Trismagia seconds before his death begins to laugh as he notices that Dante realizes the answer himself something he couldn't and Trismagia asks Dante...
"When the time came do you think Sparda has ever killed a human for the sake of mankind?"
Then swooshh...Trismagia bursts into a white flash just like in the game.