She wants to start a harem for Izuku!

"Do you want me to make her yours?" Momo asked Izuku bluntly.

"...WHHHHHHAAAAATT!?" Izuku shouted, his brain practically breaking at the idea.

"You heard me, Master!" Momo giggled. "I can tell, you do kind of like the idea!"

"But, but, wait!" Izuku panicked. "You're my girlfriend! Why would you want to include other girls into our relationship!?" he asked, mentally panicking at the idea of having two girlfriends. Momo was right, it had its appeal, but it was a lot to process at the same time. Just when he thought he was getting used to her antics, too!

"I thought you would have known what I'm about in terms of our sexual relationship by now, Master," Momo teased. "Your pleasure makes me happy. Ensuring you have more girls to help me make you happy is better for me. Plus, I was bisexual even before I became a genie, albeit not aware of it, I hadn't really explored my sexuality, but becoming a genie would have made me bi by default if I wasn't. So I'd enjoy exploring relationships of my own with any other girl you had."

"Wait, but, um... It's... Highly unusual to have multiple sexual partners!" Izuku sputtered.

"Not completely unheard of though, just slightly rare, given monogamy is still the norm," Momo replied. "The worst you'll get is some raised eyebrows."