walkthrough video here

If you killed Geni prior to getting the tome you will have to go to mibu village and make your way to the cave entrance at the back of the village and kill the corrupted monk, he gives you breathing technique to dive, then go to senpou there is a lake near the top of the mountain surrounded by wolves and monks dive to the bottom the tome is there,......secondly if the infested monk is not sitting at the altar it's probably because you have beaten the the guardian ape and corrupted monk I believe and should now be allowed to go to the illusion and fight the folding monkeys for the memory and puppateer ninjutsu ....should really all be a domino path, hope this helps, if not I apologize.

Which old lady and exactly where?

What am i to do if the old lady isn't on the bridge in Ashina castle should i do something for her to appear?

You can get the tome by talking to the Infested Monk in the Main Hall before fighting Genichiro. Just discovered this. The monk is friendly and seems to be regretting something.

I am in NG+. I defeated Genichiro so the monk doesn’t give it to me (or talk to me). But it’s also not in the pond near Temple Grounds idol. Bug or am I missing something?

Uhh...I gave the chapter to kuro...what do I do now? was talking with him and the option came up so I just pressed it.

hey guys! i find this item at temple grounds idol! when travel there dive into the water and you find it

I've reached the Great Sakura Idol at Fountainhead Palace. I just found out about alternate endings. I must've either missed the friendly and regretful monk or I didn't talk to Kuro at a specific time after defeating Genichiro. I found a Prayer Bead at the bottom of the Temple Grounds Idol pond. Nothing else. The Divine Child is permanently sick and will not give me anymore rice until i obtain this item. I guess I'll have to do it in ng.

Deleted the part about giving it to Kuro after battling Inner Genichiro as it's simply not true.