SPOILRS AHEAD: DONT READ IF YOU DONT WANT TO BE SPOILED.
DMC has ripped off many things.
DMC 1: Inuyasha
DMC 4: Bleach
DmC: Vergil downfall - Bleach
Though i thought Ninja theory would be more original, but i think (not stating as a fact) that it is most likely a Bleach rip off. This just my opinion, and i will elaborate so that you guys can understand how i come to the conclusion that "It's a Bleach rip off".
1. The place where Vergil foughts HVergil looks very like Hueco Mundo (hell in Bleach):
1:16
2. Then there is the term "Hollow Vergil", very weak basis for calling something a rip off as you guys pointed out.
3. Then there is the simarlities between Downfall and Bleach:
First let me explain what "hollows" are in Bleach. They are basically human souls who have lost their hearts because of despair or remain in human world to long(Basically if you stay around in human world after death you wil become a hollow, your "chain of hollow" keeps tearing apart) . Therefor they have a hole in their chest:
They are corrupted human souls.
2:39 Inoue tells his brother who had turned into a hollow to leave Ichigo and others alone. His brother did not move on to Heaven (soul society) as result of this he was phrone to becoming a hollow. He didn't move on because he loved Inoue and wanted to watch over her (their parents were abusive, Inoue brother shielded Inoue from all that and they left home).
When Vergil in Downfall looses his heart he blames the people who cares about him. Similar to Inoue's brother when he turned into a hollow. So what can you conclude from that? Similarity in behavior. Because Vergil did cast away his heart in Downfall.
Moving on...when Vergil used Yamato in beginning of Downfall to summon Dobelganger, the Dobelganger absorbed his amulet. Basically it seems that Dobelganger wanted to take over the body of Vergil. I dont know how Dobelganger had a concious because it was just a ability but we will leave that for now.
In Bleach there was THREE souls in Ichigo's "soul world":
Ichigo, Hollow Ichigo(a evil fraction of Ichigo that manifested in him when he tried to get his Shinigami (deathgod) powers back) AND Zangetsu. Zangetsu was Ichigo's Zanpaktou (sword). A Zanpaktou abilities and shape is based on the shinigami's soul. And a Zanpaktou's soul is a creature that lives inside the shinigami, while it's physical body is the sword the shinigami is wielding.
Hollow Ichigo was created in the process when Ichigo got his shinigami powers back by getting his Zanpaktou back. From then the balance was such: Ichigo was the one with the crown (the soul who controlled the physical body) while Zangetsu and HollowIchigo were in the depths of Ichigo's soul.
Since HollowIchigo was created when Ichigo got his shinigami powers (which came from Zangetsu), HollowIchigo was intially A PART of Zangetsu. Overtime HollowIchigo power increased, and the role between Zangetsu and HollowIchigo reversed. "I became stronger, therefor Zangetsu became part of me".
And here comes the relevant part, when Zangetsu became part of HollowIchigo: Everytime Ichigo tried to channel out the powers of Zangetsu through his zanpaktou - HollowIchigo would try to take controll of him:
5:45
When Vergil used dobbelganger ability through Yamato in beginning of Downfall, and it allowed HollowVergil to absorb Vergils amulet similar to how when Ichigo used Zangetsu's abilities (who had become a part of HollowIchigo) it allowed HollowIchigo to influence Ichigo by for example taking over his body. Zangetsu was source of Ichigo's shinigami abilities. And it seems that the amulet that was snatched by Dobbelganger represented the powers of Vergil in downfall.
4. There is also the similarities between the scenes in Bleach and Downfall:
5:32
4:01
5. Using the colour white to represent a evil side or thing.
I could be wrong, but i can't help but feel strongly that this is a Bleach rip off.