I don't know why the Chinese team has nominated only three players.
Ranking-wise, they look no match for Japan, but you can never underestimate anyone at Davis Cup! Two of the players are young, upcoming players, so their ranking may not reflect their true form.
Kei said at a press conference today that his arm is not yet 100%, and MR scan found that he had tendonitis on his arm. But he said it's definitely getting better and that he can play DC.
Good luck to Kei and all his team mates!