Akechi Goro
The two originally first met in middle school. Goro was one of those people that caught her eye. Mina would talk to him from time to time, but when it was time for her to move again, she suddenly distanced herself from Goro without explaining why. Goro had been able to deduce that she was getting ready to move again. After he confronted her about it, she essentially cut him off out of guilt and fear.
Mina continues to move until she's finally given consistency at Kosei High School. By this point, Mina still thinks about Goro and feels strong guilt over how she left things between them. So she vows to do better. Which why she pushes herself to let Yusuke get to know her properly.
While looking into the mental breakdowns by traversing the metaverse alone, she finds a familiar face she never thought she'd see again. Akechi Goro. She had heard of his names on various news outlets and even amongst students, but she didn't expect to see him again after a few years in the metaverse of all places. Mina doesn't bother sticking around, too off put by the circumstances.
Later on, when the phantom thieves become a primary target, the two are reunited. When she's away from the others, Akechi pulls her to the side, and questions her. Why she's even working with them.
For a while, their relationship is strained by unspoken feelings. It is only during the summer that Mina attempts to rekindle things. This is because she learns that Joker hangs out with him. She apologises for how poorly she handled things back in middle school. Akechi accepts her apology, but asks if she'd do the same thing again— disappear without a word. The question makes her emotional, but she shakes her head.
After that, the two can be seen in Kichijoji together sometimes. During Akechi's temporary alliance with the Phantom Thieves, Mina's devotion and appreciation towards Akechi shows a bit more openly. Akechi isn't as open about his feelings through his words, but it'll show through his actions especially during battle. More notably if Mina is on low HP or is fallen.
It is later revealed the two began dating sometime in early August. Which explains why the two seemed visibly closer even if neither of them confirmed anything. Mina's love for Akechi is loud while his is more so a quiet yearning. The two aren't open about the romantic relationship in public due to Akechi's popularity.
After the events in Shido's place, it becomes clear just how deep her love for Akechi went from how she actively grieves. During the bonus semester, the two can be seen hanging out even more.
Yusuke Kitagawa
The two are very close friends that attend the same school. Yusuke caught Mina's eye, giving her the courage to strike up a conversation— something Mina rarely ever does. The two regard each other as found family. Mina deeply appreciates her close bond with Yusuke. Mina regards Yusuke as her first real friend.
Joker
Despite Mina joining the Phantom Thieves pretty early on in their career, Joker doesn't get the chance to fully connect to until weeks after Madarame is taken care of. The two are close friends after Joker spends more time getting to know her. It is Joker that helps her learn to be more comfortable with expressing herself even if it means it's not acceptable by society's standards for her. Mina admires him a lot and is often seen confiding in him whenever she has trouble.