Fish of Darkness

Fish of Darkness (ヤミ金魚, Yami Kingyo) is a Mysterious Being and the head of Niya Niya Loans.

Appearance
As a human, he was light-skinned with light brown, combed back hair, short facial hair, and wore a dark purple suit with a light purple, almost white shirt underneath with frilled sleeves. He also wore two white scarf ties around his neck, multiple rings, and large circular sunglasses.

As a Mysterious Being, he becomes a pink, anthropomorphic fish wearing black BDSM equipment.

Road to Hero
As a human he had an impulsive desire inside him to buy out all the stores in Z-City, through his criminal organization that was based in Saitama's old apartment complex. After Saitama figured out their base, he beat up all his lackeys and was informed that Saitama was heading to confront him. After Saitama angered him, he triggered his transformation into a Mysterious Being called Fish of Darkness. After a brief battle, he lost against Saitama and was handed over to the police for a reward.

Abilities and Powers
Fish of Darkness is a fairly powerful being. He was strong enough to give Saitama some trouble, albeit this was still while he was in his early stage of training, and he was quickly defeated after Saitama became pumped up for the reward money.

Physical Abilities
Enhanced Speed: Fish of Darkness is fairly fast. He is a able to attack with his whip in rapid succession.

Egg (Ballgag) Spit: Fish of Darkness demonstrated the ability to shoot out eggs (ballgags) from his mouth.

Equipment
Whip: Fish of Darkness uses a whip. He is fairly skilled with it as he was able to give Saitama a hard time, but it should be noted that Saitama was still fairly weak at this time.

Trivia

 * Fish of Darkness is the first mysterious being whose transformation process was shown on screen, although the "transformation" process was quite different from other transformations shown later in the series.
 * When he saw Fish of Darkness take on his new risqué outfit and appearance, Saitama doubted that the man had actually transformed from a human into a monster like he had intended to, due to Saitama having previously watched a program on television about how organisms undergo metamorphosis.  Instead, Saitama hypothesises that, rather than being a monsterized human, Fish of Darkness was merely a weirdo who had become an even weirder weirdo, thereby becoming a pervert.  It is unknown whether there is any truth to Saitama's conjecture.