
a romantic relationship with Tatsumaki
Let's say you manage the impossible and win her heart. What would it really be like to have a relationship with Tatsumaki? Many people have a distorted view of the character, seeing her as an adorable tsundere who's just looking for love, when in reality she's very different.
To begin with, Tatsumaki, being a public hero, so strong and with so many enemies, would make you her weak point, and you'd be in constant danger from all the organizations trying to harm her.
You'd also have a huge responsibility towards her, as you'd become her Betty Ross. You'd be one of the few people capable of calming her down and preventing her from causing disasters.
We already know she has a very distorted view of love, as she's quite possessive, intense, and overprotective of the people she loves, especially if she feels they're in danger. The only reason she gave Fubuki more freedom is because she also has powers and equipment, and because she believes Saitama is protecting her. But you don't have powers, and Saitama isn't watching over you, so if she acted that overprotective with her sister, you, lacking powers, would be even more protective and possessive.
Tatsumaki also has a very volatile temper, so you'd have to know what to say; not because she'd hurt you, but because she'd take it out on others.