Devils and Humans can combine in chainsaw man to form two different creatures: Devil Hybrids and Fiends. It is hard to differentiate them because of their similarities and the rare nature of hybrids. They’re mostly similar but there are a few key differences that help them distinguish from one another and even from the devils who created them.
Devils are unique creatures who possess supernatural abilities to reference future devils, who can see the visions from the future.
Because of contract formation, humans can form contracts with the devils and use their powers but the true strength of the devil is determined by how much fear their name creates. Gun Devil can be seen as an example, he became so powerful that every nation restricted the news related to guns to normal humans and even implemented strict gun laws to control the fear of guns. Devils are technically immortal, when they die in hell they appear in the human world and when they die in the human world they appear in hell.
If any devil possesses a human corpse, it becomes a fiend. Mostly the devil stays in full control but in some cases, fiends capture most of their host’s brain, this is exactly what Aki did after he became a gun fiend. When it comes to strength fiends are significantly stronger than humans as they have their devil’s power at their disposal, but they’re still not as powerful as their original form. Fiends cannot make any contracts with Devils and Humans.
There are many fiends in the series but its power has gained popularity among most fan lists. Keeping her charm aside, she’s a blood fiend who can manipulate the blood freely to transform weapons. Like all fiends have a unique head feature, she has two horns that come out from the top of her head, the size of these horns is dependent on the amount of blood that she has consumed.
Beam, the chainsaw devil who worships the shark devil, has a head that resembles the shape of a shark, he can also swim through solid objects and he can also change into his original devil form which is uncommon in the species.
On the other hand, Devils are rare, as only 4 of them have appeared in the series so far. They appear only when a devil fuses himself with a human. Unlike fiends, the Hybrids have human appearance and consciousness but they have more strength and ability when it comes to transformation. Just like Devils and Fiends they can restore their health by drinking human blood.
Denji is the best example of a Devil Hybrid and shines a light on most of the peculiar questions about this fusion. Just before combining with a dog-like chainsaw devil, Pochita. He was left for dead with a damaged eye and a heavily wounded body. The contract allowed them to fuse which healed him completely and grant him the power to pull out chan=insaws from his head, legs, and arms. As we saw in recent chapters he became more efficient with his ability to transform into Chainsaw Devil and lose most of his human form.
All the devils in the series have unique switches or triggers that they use for transformation. Reze, the Bomb Devil pulls out a grenade pin from her neck. Denji, pulling a starter cord from his chest to rev up his inner chainsaw. Katana man transforms by pulling his blade full of his left hand. The last and fourth Hybrid, Quanxi, a Chinese devil hunter pulls an arrow from her empty eye socket.
From a birds-eye perspective, Devil Hybrids could be considered as a full version of Fiends. The most measurable difference lies in their strength. Becoming a fiend is seen as the last resort but given the gravity of the strengths and abilities, it becomes a no-brainer that both forms are a serious force.