If you're looking for manga similar to Toushin Devilman, you might like these titles.
This is a shounen manga about a high school senior named Taketo Iwase and a dog named Salsa. As they set off early on to resolve a problem with a criminal that Toshifumi (Taketo's brother) is having, Taketo sees that there is more to the dog (that can communicate in the human language) than meets the eye. Together they solve a number of troubles and also meet other different species (cat girls, dogs, birds, etc). Wild Half has some very funny gag lines, some moving plots, helpful morals, in short, a little bit of everything packaged into one.
The drug 'Nitemare' gives a drastic impact, changing a human physical to a gigantic creature. Then a man appeared to stand up against these creatures for the sake of prosperity and to prevent misfortunes of mankind.
Yuu has been waiting for the release of the computer game White Earth, which was developed in total secrecy and had its release date postponed for unknown reasons. He finds out from some friends that he can download it from the game's official site, which results in a child coming out of his computer.