That guardian deity so probably caused that injury on Mao to prevent em from leaving. Going for the yuri sister route/Mao goes back to a guy/step sister route, but I do like the best friend. Though it would still be kinda odd for the friend to go for his buddy now that his buddy is a girl. Like if my best friend turned into a girl, I still wouldn't be able to see him/her as more than my bud lol.