[Sunred]

So Zeronos and Deneb. There are two sets of motifs behind these two, one of them which I will share way later when you get through 20 more so episodes. The other one that I can share right now is that Yuuto/Zeronos and Deneb are based off of the Japanese lore of Ushiwakamaru(pronounced ooh-shi-wakamaru) vs Benkei. It is about how the hulking Benkei tried to take down Ushiwakamaru so that he can be the 1000th opponent he defeated and take his weapon to add to his collection, but Ushiwakamaru nimbly dodged his attacks to the point where Benkei gave up in the end. There is also a children's song about it but seems like the actual incident is still pending on whether it actually went down like that. Think of it as Kraven vs Spidey but Kraven eventually went on to be his humble servant after admitting defeat.
Now this song has historical ties in that it is based off specifically on Yoshitsune and Benkei, two historic figures from the 12th century. Yoshitsune was a commander and Benkei was a warrior monk who went on to serve Yoshitsune, and Yoshitsune had another name he went by when he was younger and that was Ushiwakamaru. In relations to that the reason Zeronos is based off a bull is because the ushi in Ushiwakamaru means bovine.
Respectufully Deneb is Benkei, and as Androzani84 pointed out previously he is also based off Karasu Tengu as well. The reason these two are Deneb's motif is because in fictional folklore Benkei is known to have ties with Karasu Tengu in fictional lore such as folklore and myths, etc.