Saitama/Relationships

King
King took credit for killing five mysterious beings that were actually killed by Saitama. This caused King to have the fame and 'fortune' as a S-classed Hero. Saitama discovered King's true personality and the secret to his success. Saitama wasn't upset or angry at King's secret and the two would become friends. Saitama would go to King's house to play video games and become frustrated at losing to King.

Fubuki
Fubuki, after her first encounter with Saitama, was sometimes seen along with King and Genos hanging out in Saitama’s abode. She is apparently obsessed in making Saitama join the Blizzard Group. Her latest attempt was to beat Saitama in a video game competition, which failed due to King’s assistance. Saitama himself declared, that he doesn't view Fubuki as a friend, but as an "acquaintance".

Tatsumaki
At their first encounter, Tatsumaki didn't think much of Saitama due to his ranking and would insult him. She was even insulted from him ignoring her. Saitama mistook Tatsumaki as a sassy child due to her small stature, and found her to be annoying.

Spoilers Webcomics:

Their next encounter would be when they 'fought' in the Psychic Sisters Arc., where Tatsumaki finds out how powerful Saitama really is. Saitama displayed concern and interest toward Tatsumaki, as he ran after her to see if she would be alright flying home with her injuries and was interested in why Tatsumaki pushes everyone away. However Tatsumaki simply yelled at him, causing him to be even more irritated at her behavior. Tatsumaki came close to revealing her past and Blast to Saitama before deciding not to.

Mumen Rider
Saitama and Mumen Rider share a mutual respect toward each another.

Saitama respects and acknowledges Mumen Rider's ability to continuously do the daily quotas of the C-class heroes, something Saitama found to be a difficult job. He also compliments Mumen Rider for putting up a nice fight against the Sea King.

Mumen Rider is one of the few who knows of Saitama's true strength and treats him respectfully as a fellow hero. He sent Saitama a thank you letter and offered to pay him dinner, where he thanked Saitama personally, further showing Mumen Rider's humble and respectful nature.

Garou
Webcomic Spoilers:

Garou displays hatred toward Saitama during their fight, seeing Saitama as the collective unfairness of the world, add that Saitama is a hero, Saitama represented everything that Garou hated and was fighting against. Saitama is responsible for defeating Garou both physically and mentally, realizing that Garou wanted to be a hero instead of a villain.

Saitama showed mercy towards Garou, refusing to kill him and acknowledging his flaws.