So yes, it really is a special blessing from the Miko. I guess he's one of her knights now, or at least her one and only knight. I like the detail that it has to be consensual, so that means the Miko can not simply select someone against their will to serve her/be her guardian.
Gotta love how Lerunda is also gung-ho about physical training. More physical fitness never hurt anybody, it will definitely serve her well. There are no rules that dictate chosen shrine maidens and saintesses and priestesses have to be physically weak with no stamina. If only she could freely use healing magic it'd do her well to learn a little bit of The Wrong Way To Use Healing Magic™.
Her friends being conscious and considerate of their innate physical differences was nice to see too. They'll all improve together, no one is getting left behind.