I think of Tatsumaki as the Anti-Saitama. Everything Saitama is, Tatsumaki is not. Examples:
- Tatsumaki belittles the weak. Saitama uplifts the weak.
- Tatsumaki was born powerful. Saitama was born weak.
- Tatsumaki has a child-like body despite being 28. Saitama has a well-built adult body but is bald at age 25.
- Tatsumaki is arrogant. Saitama is humble.
- Tatsumaki flaunts her power. Saitama never flaunts his power.
- Tatsumaki is cruel. Saitama is merciful.
- Tatsumaki alienates other people from her. Saitama draws other people to him.
- Tatsumaki is one of the most revered heroes despite being not very heroic herself. Saitama is the most reviled hero despite being very heroic.
- Those closest to Tatsumaki are scared of her. Those closest to Saitama admire him.
- Tatsumaki secretly wants friends but is terrible at making friends. Saitama doesn't want friends at all but keeps making more friends unintentionally.

ONE seems to have almost unintentionally created a very unique character dynamic between these two. They almost feel like the two sides of the same coin in more ways than one. I don't ship them, mainly because they are as completely different as they are very similar, but it is fascinating regardless and I want to see where this will go.