Cronus the Umbreon

This Umbreon is a Dark-type Pokemon owned by Lilith and was the first Pokemon she revealed to possess. He has appeared alongside Lilith in the first episode Pokemon - I Choose You!. He is infected with the "Pokehuman Virus" which makes him able to change into a human at free will.

Personality
Cronus is extremely protective of his trainer, Lilith. Cronus protects her from people, such as Brock, and Pokemon alike. Cronus also has romantic feelings for Lilith, shown when he was cuddling up to her when she was having a nightmare.

Cronus has always been there for Lilith and also takes a leadership position for the team. He is smart but serious, especially when it comes to Lilith. Just like Lilith, however, he doesn't seem to enjoy battling except when he is protecting Lilith, to when he is extremely serious and feels that its no joking matter. He is extremely obedient to Lilith, obeys her every command, and rarely leaves her side. He is also a constant target for Team Rocket. They try to capture him and Pikachu, but on the few occasions that they do, their plans are always thwarted by Ash and his friends. Even after getting out of their traps, avoiding capture, or that he wasn't part of their schemes, Cronus also thwarts his enemies by attacking or getting rid of them using his Psychic attacks. He is very swift in battles as well.

Like his trainer, Cronus shares Lilith's love for helping people and Pokemon in need. He himself, however, doesn't understand the concept of love that much as he has trouble understanding his feelings for Lilith.

Cronus is mostly quiet and likes to keep to himself most of the time. Even though he barely shows his emotions, he cares deeply for Lilith, whom he admires for her kindness for everyone. Still, he dislikes Trainers who don't fit his expectations, especially those who are selfish. This also happens in Evolution by Fire!, in which Cronus Hates Shamus for abandoning Tepig and his cruelty behavior which he convinces Tepig to fight his former trainer, even though he keeps his loyalty to him.

Just like Sceptile, Buizel, Hawlucha, and Greninja, Cronus is very cool, calm, collected and serious.

Pokemon Form
Cronus is a quadruped mammalian Pokémon that resembles a black cat, black rabbit, or a black fox. Cronus has mainly sleek black fur with luminescent blue rings encircling his ears and tail and round blue circular patterns on his forehead and on each of his upper legs. The rings glow when under the influence of moonlight. His physical characteristics are vulpine-like, but also feline-like as well, with a short muzzle with a small triangular nose. He has golden eyes, and unlike his fellow eeveelutions, he also has visible black colored oval-shaped pupils. Cronus has a slightly bushy black tail with a single blue ring encircling his thickest part; the tail thins out at the tip. Cronus has small sharp fangs, seen when he opens his mouth.

Human Form
As a human, Cronus has mainly sleek black hair with luminescent blue rings encircling his ears and tail and round blue circular patterns on his forehead. He also has a jacket with blue rings resembling those of his Pokemon form. He has golden eyes like his Pokemon form with the same pupils. Cronus has a slightly bushy black tail with a single blue ring encircling his thickest part; the tail thins out at the tip. Cronus has small sharp fangs, seen when he opens his mouth.

Natural Abilities
Cronus can spray a cloud of toxic gas from his sweat glands when agitated. Also, since he's a fully evolved Pokémon, Cronus can learn the moves Hyper Beam and Giga Impact and even though Cronus is a Dark-type Pokemon he knows the move Psychic. Although Cronus looks small, he has a strong endurance.

Information
When this Pokémon becomes angry, he pores secrete a poisonous sweat, which he sprays at his opponent's eyes. When darkness falls, the rings on his body begin to glow, striking fear in the hearts of anyone nearby. The only one not affected by this is Lilith. On the night of a full moon, or when he gets excited, the ring patterns on his body glow Blue. Cronus evolved as a result of exposure to the moon's waves. The light of the moon changed Eevee's genetic structure. This Pokémon is nocturnal. Even in total darkness, his large eyes can spot his prey clearly. He hides silently in darkness and waits for his foes to make a move. With his black fur, he blends into the darkness. He bides time, and when prey appears, this Pokémon goes for its throat, and then eats it. At the moment it pounces, the rings on its body glow dimly but ominously. When exposed to the moon's aura, the rings on his body glow faintly and he gains a mysterious power.

Trivia

 * Cronus is the only non-Psychic-type Pokémon with the ability Synchronize.
 * Cronus is the only Eeveelution with black pupils. All the other Eeveelutions have a white light in their eyes resembling pupils.
 * Cronus is possibly a Yandere, but that's up to debate.