Hello, I'm Dr. Van and I will be glad to answer your questions today!
Does Titan go outside often? Are there other cats in the house that do not get along with Titan?
One thing I am concerned about here is a cat bite. When these cats get in fights, the bite wound is often very small and hard to find. These cats get sick and develop a fever. Over time, the bite wound turns into an abscess and is eventually able to be seen.
There are certainly other causes of an infection causing fever and lethargy in cats, however in these younger ones, it is usually some sort of trauma like a cat bite (as opposed to a kidney
infection, urinary tract infection, etc.).
I would bring him to a vet to get checked out and to get him some much needed support. They will likely get him some antibiotics as well as some antiinflammatories to take down the swelling and make him feel better. Fluids and B vitamins may also be necessary to help him convalesce.
So I think with a fever this high and lethargy, his best bet is to go to a vet for an exam and medication.