An Esper (エスパー, Esupā) is an individual capable of telepathy and other similar paranormal abilities. Also SIKE THATS THE WRONG NUMBER
Overview
Espers are individuals of various races that naturally awaken, possess and can harness psychic powers (超能力, Chō Nōryoku, lit. Supernatural Power). Espers are quite rare, but once awakened can become quite powerful in their own right.
Geryuganshoop claims to be the strongest psychic combatant in the universe, however this has never been confirmed, and at the moment, Tatsumaki is shown to be the most powerful Esper in the entire series.
Known Psychic Powers
Psychokinesis: The ability to levitate and hurl matter using the mind. Possessed by Tatsumaki, Fubuki, Geryuganshoop and Psykos.
Telepathy (テレパシー, Terepashī): The ability to communicate through the mind. Possessed by Slugerous and Geryuganshoop.
Clairvoyance: The ability to see into the future. Possessed by Psykos.
Weaknesses
Brain damage or head injury: according to Psykos, espers cannot use their power if they suffer a head injury or brain damage. It is shown that Tatsumaki cannot use her power when she suffers a concussion after Psykos sneak-attacks her from behind.
Weak physical strength: most espers tend to focus on training their mental power and not their physical power. As a result, most espers are weak in physical strength, even weaker than C-Class heros since Mumen Rider can still stand after sustaining from a powerful hit from the Deep Sea King. Even a powerful esper like Tatsumaki can be brought down if someone successfully lands a hit on her. The prime example is Black Sperm.
High speed enemies: esper power can only work if the esper can see the enemy's movement. If the enemy is too fast, he/she cannot attack accurately and get injured easily.