Onuma Den is a Cobra Therianhtrope and a former member of Sumitomo Zaibatsu. He used to be one of Shinna Ryuji's gang members until his defection
He has a small build, black hair and while in his hybrid form, his lower half is replaced with a cobra's, his tongue becomes snake-like and turns purple, his teeth are replaced with fangs and his eyes glow green. In his full hybrid form he becomes a human sized cobra, his top half becomes that of a snake. Now sporting a flap like 'hood' that are trademarks of the cobra as well as poisonous fangs. In this form his bulk and length make him bigger than most of his opponents.
After the 2 years timeskip, his appearance hasn't changed much other than now he wears an eye-patch over his right eye.
He is a sadistic lecherous person who prefers to have sex than actually fight. The cobra part of his body either helps with him weakening foes or makes it more enjoyable for him. He has raped one unnamed women and attempted to rape or threatened to rape Inaba Ui, Nakanishi Eruza and Uzaki Hitomi consecutively. He does respect the hierarchy of his group, however. He fears Kaede and does his best not to incur her wrath. He may well look up to Shinna Ryuji he refers to him as Brother Ryuji or 'bro' for short and seems to listen to him.
However in the manga, after his defeat against Hitomi in Destroyale his personality takes a turn for the better. He left his gang went back to school and currently is now working for the Ishida Zaibatsu as an Internal Inspector of the Association. He holds no hard feelings towards Hitomi despite losing an eye to her, and is actually grateful for the change his defeat caused.
- Snake Shackles/Snake Chains/Jabaku -- Using his coils he can wrap up opponents. This can be used to break bones, hold competitor's in place or throw them into/against things.
- Cobra Mist -- Using his venomous fangs he can spread a poisonous mist that when inhaled incapacitates his opponents. It is unknown whether it has the ability to kill opponents with no immunity. His Cobra Mist is so powerful it was able to take down 4 brutes as well as the camera crew.
- Cobra Cannons -- (Graphic 18+) Chapter 15 of the manga and episode 6 of the anime for more information this ability.
- Enhanced Endurance and Durability -- Being part cobra, Onuma was relatively unaffected when he was castrated and later bisected by Hitomi, although he was still left in agony afterwards.
- Nakanishi Eruza VS Onuma Den and Kazama Kaede (Undecided, Interrupted by Uzaki Hitomi)
- Onuma Den and Kazama Kaede VS Uzaki Hitomi and Nakanishi Eruza (Loss, Prolonged fighting ending in Fatality.)
- Onuma was a member of a gang called "Reptia" founded by Shinna Ryuji. He believes it's Kanto's most powerful gang.
- Some animals are resistant to the effects of cobra venom such as honey badgers/ratels, mongooses and opposums.
- He's shown to be more lecherous in the anime adaptation attacking Inaba Ui in the bathroom in an attempt to rape her this does not appear in the manga.
- His language is used in a way that might be less offensive in the anime adaption such as swearing at Nakanishi Eruza and Uzaki Hitomi rather than calling them whores and harlots.
- He claims reptiles are superior to mammals despite loosing to a mammal less than half his size. He lost his manhood, a good amount of his organs along with his pride.
- His surname is sometimes translated as "Ohnuma"