Black Sperm

The following section contains Webcomic spoilers. You have been warned manga-only readers.

Black Sperm (黒い精子, Kuroi Seishi) is one of the few Dragon monsters in the Monster Association, who first appeared during the S-Class Heroes' attack on the Monster Association.

Appearance
his plain appearance and small stature

Monster Association Arc
Black Sperm appears when Busaiku is separated from Garou. Black Sperm chasing after the kid in hopes of killing the child. Atomic Samurai steps in, but Black Sperm soon overwhelms Atomic Samurai due with his ability to split into numerous versions of himself, as well as regenerate whenever.

When Tatsumaki destroyed the Monster Association HQ, Kuroi Seishi and several other Dragon level monsters emerged from the rubble to attack her. After Psykos temporarily cut off Tatsumaki's psychic power, the monster grabbed her in a giant arm while attempting to crush her. The esper was saved by Genos, though the cyborg immediately had his arms ripped off by Kuroi Seishi and Gums. Once Bang joined the fight and effortlessly killed two of the Monster Association's remaining members before being knocked out by Homeless Emperor, Kuroi Seishi took this opportunity to knock Bomb unconscious.

After King managed to buy some time against the remaining monsters, Tatsumaki began to recover and turn the tide of the battle. In an attempt to defeat her, Kuroi Seishi fused one trillion copies of himself into the much stronger Multicell Seishi, though the newly formed fusion is effortlessly killed by the hero. Sending a thousand copies of himself to perform a kamikaze attack against Tatsumaki and buy about 20 seconds, Kuroi Seishi takes Busaiku hostage, forcing the heroes to simply stand and watch as he fuses 10 trillion of himself into his ultimate form, Ōgon Seishi. This new form proves incredibly dangerous, as Ōgon Seishi takes down Tatsumaki so fast, nobody else could even follow his movement with their eyes. However, this victory proves short lived, as the newly mutated Garou shows up, destroying 99 of the 100 remaining copies of Kuroi Seishi and killing Ōgon Seishi after a brief battle that none of the heroes could even see. Now down to only one life, Kuroi Seishi slips away to watch the battle from afar. The next day, after encountering Saitama, Kuroi Seishi and Overgrown Rover follow him home as pets. The two formerly dangerous monsters are currently entrusted to Butterfly DX and Chain'n'Frog due to Forte losing a bet with Saitama.

Abilities & Powers
Being a Dragon level threat, Black Sperm is quite powerful

Physical Abilities
Immense Speed & Reflexes:

Enhanced Strength:

Enhanced Durability:

Shapeshifting

Size shifting

Regeneration

Fighting Style
Merge: Black Sperm permanently combines his cells to form a more powerful version of himself. As the
 * Multi-cell Sperm: Any number less than ten trillion of cells that merge. The strength of this form has yet to be observed as the only Multi-cell Sperm observed was quickly taken out by Tatsumaki.
 * Golden Sperm: Requires at least ten trillion cells to create. This form is able to defeat an injured Tatsumaki.

Major Battles

 * Black Sperm vs Atomic Samurai
 * Black Sperm, Psykos, Gums, Homeless Emperor, Evil Natural Water, Fuhrer Ugly vs Tatsumaki
 * Black Sperm vs Genos