Board Thread:Questions and Answers/@comment-116.65.70.72-20130325123118/@comment-5527544-20130703100830

Ultraman and Hayata for whatever reason didn't maintain their merger. Ace and Seiji did and so did Jack and Hideki, why Shin and ultraman didn't is unknown but Saga takes place long after they last merged. It was already stated that Hayata most likely died of old age before the first Zero movie, he's just using that form to honor his memory.