Ryuk tattoo means ruthlessness. In the death note, compared with other gods of death, Ryuk seems to have no taste of "human", no protective things, and few principles. His indifferent attitude shows that he is not even interested in being the master of the game. Give notes to anyone who has the potential to make the game interesting.
Ryuk is a god of death who really envisages human beings as ants. When the role he chooses can no longer bring the brilliance he wants, he will abandon it indifferently. At this point, night God moon is very similar to him. On the other hand, if one day Chuck is worthless to Yue, with Yue's character, he will also abandon him without hesitation.
Source: @rebecamarquet