One-Punch Man: Why is Tatsumaki so Much Stronger Than Her Sister?

gamerant.com:

Amidst the high-speed slashes, laser beams, and power punches, there's a pair of sisters that manage to make a name for themselves in the chaotic world of One-Punch Man. Their names are Tatsumaki and Fubuki, and they are known as the «Psychic Sisters».

However, despite being sisters who use psychics as their primary weapons, both Tatsumaki and Fubuki couldn't be more different from each other. They differ not only in terms of personality, but their physicalities are also the polar opposite of each other. That being said, the biggest difference between them is the level of strength. Tatsumaki is way more powerful than her little sister.

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Tatsumaki is the 2nd ranked S-Class hero according to the latest assessment by the Hero Association. She is second only to the legendary S-Class Hero, Blast. She is regarded as the strongest esper in history. Her psychic power is so great, she can easily level an entire city without breaking a sweat. That is why she earned the moniker «Tornado of Terror».

However, contrary to her overwhelming power, her appearance is similar to that of a teenager. She is a petite woman with medium-length hair and slim figure. That is why she is often mistaken as a little girl, or as Fubuki's little sister, which is one of the things that can easily rile her up.

Excluding Blast, for as long as she can remember, Tatsumaki never met anyone who are stronger than herself. This is the reason why she often dislikes working in a group. Because to Tatsumaki, rather than helping, other heroes would only end up as a hindrance that would jeopardize her mission.

That being said, she would never let anybody die on her watch. Just like during the final battle