Mira fits very well as the "childhood friend that became more than just friends".
Well, Arianna too. Just wondering why we've never seen Mira and Arianna interacting so far.
Arenfield is a village, so everybody knows everybody.
Let's have a look at the younger generation. We have:
boyz:
- MC aka The Dude.
- Rick, MC's best buddy and Arianna's brother
- Henry, Penny's (now) former fiancee (well done, MC!) and Dave's best buddy
- Dave, baron's son and Frisha's (now) former fiancee (well done, MC!)
chicks:
- Mira, MC's childhood friend and more than that since the beginning
- Frisha, Mira's older sister
- Melissa, John's daughter and Mira's friend
- Arianna, Rick's little sister and MC's childhood friend
- Natasha, orphan - if I remember well - raised by Father Lewd and Athia's priestess
- Penny, lost her family during the war and (now) former Henry's fiancee
- Julia, baron's maid and Dave's half-sister
- Tia, half-orc and village's outcast
- Anya, we don't know anything about her because she never interacted with anybody and no one ever mentioned her (and this is a mistake made by the Author)
Kate doesn't count here because she isn't born in the village (she comes from Kirlic). Same with Ophilia and Liandra.