Hotaru is from the realm of Seido, also known as the Orderrealm. The inhabitants of this realm have a strict belief of order and if a rule is broken, the punishment is extremely harsh. Hotaru is the commander of the Seidian guards and will do anything he sees fit to preserve order.
Hotaru met Shujinko when Shujinko needed help protecting a city in Outworld from Shao Kahn, whom would send Baraka to slaughter everyone there. Shujinko told Hotaru that he needed him to protect the city from Shao Kahn to save innocent lives. Hotaru accepted as he saw Kahn as a chaotic ruler. Hotaru would protect the city, but would take it for himself and make it a city of strict order.
Many years later he learns of the return of Onaga the dragon king and he believes that Onaga would bring order to the realms. Therefore he helps Onaga's forces attack and pursue those that would oppose and seek to destroy the dragon king, like the lin kuei grandmaster, sub-zero.
Hotaru appears to be a tall, buff, Japanese man with white hair and pure white glowing eyes. His face appears ageless given that Seidians have extremely long lifespans and it is said that he is thousands of years old. He wears black and gold armor with a red loin cloth, and two red samurai flags on his back.
In his alternate costume he looks the same, except he now is wearing a traditional Seido guard battle helmet.
At Hotaru's mortal kombat deception ending it is said and shown that hotaru captures the lin kuei and brings him before the dragon king. Onaga's judgement of the lin keui was quick and ordered the seiden guardsman, hotaru pick his punishment for sub-zero, this punishment was DEATH. Sub-zero's fate would be a reminder to all the other warriors that would seek to challenge the dragon king.
When he defeated blaze the godlike energy transformed the seiden guardsman into a pure being of order. All would then bow before him or be transformed by his gaze. But there was one whom Hotaru would see pay for his crimes against all: the Cleric of Chaos, Havik. The light of Hotaru poured into Havik's mind and transformed him into an agent of Order-Havik was now transformed into hotaru's second in command.
Hotaru's main fighting style is Pi Gua, a Chinese fighting style which focuses on strength and striking attacks. It is the main fighting style of the Seidian guards.
Grasshopper: An attack which was very similar to liu kangs bicycle kick except hotaru jumps up into the air and kicks his opponent sideways.
Lava Burst: He throws a magma ball to the ground,ascending his opponent into the air, leaving his opponent wid open for an attack.
Fury Punch and Escape: Hotaru dashes forward with a straight punch with a streak of magma trailing from his feet, then slides back to his original position.
Quick Tricks: Hotaru does the same animation as the Fury Punch and Escapes, only this time he slides past the opponent and appears behind them.
Triple Neck Snap: Hotaru kicks the opponent in the thigh, causing them to kneel down as Hotaru takes his hands to the opponent and begins snapping their neck. He simply does not stop as he tries two more times, the third one strong enough to make the corpse flinch from the intensity.
Body Slam: Hotaru takes his opponent's leg and begins slamming his opponent around, causing blood and guts to spill out. A third time, he slides the opponent's body and slams them, causing their entire body to explode.
Hotaru takes his hand to his head and grabs it. He then, with a swift pull rips his head off along with his spine being torn out of his body as well. He crumples down onto the floor, dead with blood pouring out of him.