Spoiler (click to show/hide):
Just thought of something, how about instead of Amaterasu having a limit on ink use, overuse of brush powers can lead to arousal gain?
He shrugs, "well, if you're going to be picking up these brush strokes like that, I figured I'll be here for the long haul, and you gotta admit, Amaterasu is a bit of a mouth full. Ammy is just more convenient." He chuckled as you mentioned you'd enjoyed it. "Well, it was pretty obvious from what I could see. So does this mean you're up for restoring the River of Heavens now?" Looking around the outcropping there is indeed nothing else to be done here. If you can't cross the river, you'd have no choice but to return to the town currently veiled in darkness.
Coming to the bank, you begin to focus the same power. This time it comes easy feeling familiar as you start to fill in the river. Brushing your tail across the ink sticks where you assume the river belongs, and when you stop, the river is restored. Issun looks over the river. "Well, that answers that. Ready for a dip Ammy? You probably could do with a bath after all." His reminder brings you to notice the cum still clinging to your chest and slowly leaking from your cunt. The tiny guy jumps up onto your tail, your shoulders, and stops between your ears. "Well, no time to lose. Gotta save those people."