Yep! He was just exhausted from the previous battle. Also Rias was little weak spirited

There are phoenix tears to heal it. Besides, in the third season Ise got healed in the battle against loki

Author promoting his own artwork. The pace of novel is slow. It has lots of slice of life moments like everyday life, some family moments. Novel will follow original plot most of the time with some minor changes in beginning of series and might be some major changes due to butterfly effect as the story progresses. Try few chapter. Liked it then add to library.

17 when he reincarnates into devil according to original plot