There are 3 reasons why she reacted the way she did:
1. She and everyone else are just THAT down bad for Kanata.
2. Obviously, no-one in that world up until that point had ever experienced ASMR before and thus, will have an incredibly strong reaction to it.
3. Kanata's Infinite Mana is at play as well, albeit unintentionally. Basically, the more magic he pours into his voice and mic, the more... powerful that tingling sensation is. On the lower end, it's quite relaxing. On the higher end, we get what happened to Mira just now, but more powerful. That being said, Kanata's ASMR is more effective against women than it is against men, for... obvious reasons. Funnily enough, there are a couple times where this has been weaponized in later chapters.