So, what the hell is happening there and how a silly jewel can protect Raphael ?
Every wizard has the ability to store elixir, this is what is in the jewel. It works the same way it does in a classic RPG by healing any injury.
There is a downside to it, Cayena has to use her blood and magic to create this, it takes a lot of time and energy. She cannot do that all the time.
Cayena will use this in the future to get her hands on someone very special.
Who is the cat ?
It seems to be a habit for wizards to turn into cats to roam around. Bayel uses this form more than once, except he turns into a "cheese colored cat". I admit I laughed at that one, which cheese pretty please !?
Of course this cat isn't a Mozzarella Bayel, it's another wizard who tries to get his hands on the Garden. As bonus, he isn't alone.
Wizards can increase their power by absorbing other wizards, however it isn't allowed by the council of wizards and anybody trying to kill another wizard is sentenced to death. Those wizards don't give a duck about it, they are already on the list but catching a powerful wizard is hard if not impossible.
Since this specific one wants the garden, the only way is to lure Bayel out to absorb him, thus using Cayena is the best way to do so.
Are Raphael and Cayena a couple ? After all she keeps pushing him away and be surprised despite his chest windows.
In the novel, Raphael doesn't learn about Cayena's life trade before a while, in fact Bayel is the one dropping the news out of worry for her.
As a reminder, Raphael doesn't trust the guy as he has the same name as the one she picked when she requested Raphael to create a fake husband for her. However the announce of her death getting closer and closer because she keeps using her powers settles this problem and from that point on cheese cat and desperate lover are on the same side. The "Cayena stop trying to did tomorrow" side.
Cayena isn't as naive as she's portrayed in the manhwa and eventually gives in, they keep their relationship a secret. There is even a comment regarding Raphael stamina being an issue as she lacks of sleep. Poor Cayena.