I do everything by myself, so if I get into I can sit for 10-12 hours and do it in one go without waiting for people to do their parts shrug Still think my redrawing is slow but I don't have any artistic talent, so it's to be expected.
Seems a bit sudden in the manga for sure, but the reasoning is gone over in the LN. Basically that piano was an extension of Nito (part of her in his eyes), so he tries to feel closer to her here by sitting down at it and plays her song on a whim.