The on-loan Sporting Lisbon striker has surprised his Norwich teammates, admits Martin.
"It is the manager's decision (whether to sign him permanently) but yes, I love Kei," Martin told the Pink 'Un. "I think he has brought so much here. He has been a breath of fresh air really.
"He has brought so much enthusiasm and sometimes it gets a little bit cynical in football and with people. But he is just enjoying every minute of it here. He is in the Premier League, he is living his dream and it's really nice to see.
"And I think he's not just a good lad, he's a really good player. He has been really effective and I think he did great for us again at Sunderland."