What to read after Nana & Kaoru, Volume 3?

After staying out in the cold for New Years, Nana is gravely ill and alone. Her mother is a part of the police force and is rarely home, so she is left up to her own devices having to take care of herself. But her situation is quite serious and even a house call from a local doctor may not suffice. It will be up to Kaoru and Tachi to help her in this time of need. But their methods may be a little more "hands on" than what may be considered normal. They are going to have to support her from the bottom up.