I do not think that Japan was thinking about relations between the two countries when it rescued the 26 North Koreans from their sinking ship. Imagine the backlash if they had not intervened. However, Japan's actions can be seen as a sign of better relations and may open the door for future discussions between the two countries about putting a long history of animosity behind North Korea and Japan.
I think this is possible. This act might help create warmer ties between the two nations. We all know that Japan and North Korean Country's have had a bad past. The two nations were not in a good relationship. But after Japan rescues 26 North Koreans from a sinking ship, there will be a good relationship finally.
With the recent nuclear test in North Korea adding to the tensions, the animosity between two nations has been steadily stoked by the communist state since Japanese atrocities in World War II.
Rice, which is the staple food in Asia, is also the main product of North Korea's farmers. Many countries boosted their sanctions against Pyongyang recently in response to nuclear and missile tests, leading to worsening lack of food in the desperately poor country.
North Korea is such a secretive and crazy country that it will take a lot more than a bit of goodwill like this to create warmer ties. It reflects very well on the Japanese who saved the 26 North Koreans but that is all. It is unlikely North Korea will suddenly start thinking other countries are nice and friendly.