Energiser

Energiser (エナージラ, Enājira) was a monster located in the uninhabited area in Z-City in the audiobook, "Sonic, becoming Saitama". He was killed by Saitama.

Personality
Energiser was confident in its abilities but was still cautious. He recognized that there were beings stronger than himself and would go into hiding to avoid attention.

History
Energiser was a powerful monster hiding in Z-City’s uninhabited zone. He was discovered by the Hero Association and was targeted for attack.

Sonic, becoming Saitama
Tornado of Terror and Atomic Samurai are tasked to eliminate Energiser, but Speed-o'-Sound Sonic, disguised as Saitama, encounters the monster first. Sonic struggles to fight the monster. Fortunately for Sonic, Saitama arrived and together they easily defeated the monster.

Abilities and Powers
Energiser fought and would have killed Speed-o'-Sound Sonic had Saitama not intervened.

Physical Abilities
Immense Durability: Energiser took several of Speed-o'-Sound Sonic's shurikens without taking any damage.

Supernatural Abilities
Energy Projection: Energiser has the ability to compress and emit energy from his hands. He has limitless energy stock, but he needs time to build energy blasts up.

Trivia

 * Energiser is the only monster Saitama and Speed-o'-Sound Sonic teamed up on to beat.