El Cazador de la Bruja/WMG

As a result of Noir and Madlax, there is an enormous shortage in Male Suit Wearing Mooks in the Bee Train universe.
They tried to find some, but only got in shots in the OP. These MIB were either killed or fled into hiding during the actual show. Thus, all they had on hand were some really bad bounty hunters, two female MI Bs, and that one arc where they actually summoned gunslinging demons as temps.

The one exception to the Great Mook Shortage was Sombrero Man.
Seen "guarding" Douglas Rosenberg's "Hypno-Chamber" in the middle of the Mexican Desert, Sombrero Man wears his suit and smokes his pipe content in the knowledge that his Magic Sombrero protects him from the wrath of hot girls with guns.
 * He is evidence that they were scraping the bottom of the barrel for mooks.

The Mysterious Masked Man in the closing credits is a stand-in for the relationship between Ellis and Nadie.
When shown with Nadie, he's flirtatious and romantic, symbolizing Ellis's growing romantic feelings. When shown with Ellis, he's generally watching her do domestic things, symbolizing the way Nadie comes to see her as a good companion and life-partner.

Witches have the unconscious ability to make people around feel attracted to them.
It's mentioned several times in the show that ancient witches were worshiped as gods. Ellis, who is said to be as potentially strong as the witches of old, also invokes this feeling in other people on a subconscious level, which is why there appear to be so many lolicons in Mexico and why almost everyone in the show likes and/or loves her, several times to an unhealthy degree.
 * That was much better than my explanation, which was simply that (as a short, blonde Canadian) she's more exotic-looking than the tall, tanned Nadie.
 * This troper thinks it's simply a matter of protective instinct. Nadie looks like a person who can take care of herself, and a potential troublemaker to boot, while Ellis pretty much screams "care for me, protect me!" with all her appearance and demeanor. Ellis is like a lost child; leaving her alone makes your conscience weep if you're not a hardened monster.

Rosenberg donated genetic material to help create Ellis and LA.
Notice how much the three resemble each other? They all have the exact same hair, and Rosenberg and Ellis both have purple eyes. Puts a new spin on the creepy way Rosenberg treats LA. In fact, Ellis and LA look like twins, which would also mean they are either Opposite Sex Clones or brother and sister.

Melissa Rosenberg donated genetic material to help create Ellis and LA.
The younger versions of Ellis and L.A. look as much like her as their older selves look like Rosenberg. Also, it's pretty obvious that while she's taken in by him, Rosenberg doesn't actually love her; there must be a reason beyond stage dressing that he goes through with a sham marriage. Also the gift of Inca rose earrings at the start of their relationship -- especially with the little speech he gave her about power and whatnot -- is highly suggestive that she might unknowingly be as much a descendant of the witches as Blue-Eyes.