In the Manga
Sai Tai Sai appears in Reload at the end of the arc "Death Match." He is seen sitting in a tree watching the ikkou drive by and commented how they have felt they are 'being watched'. He remarks that it seems they felt his presence.
He appears mysteriously in what appears to be Goku's dreams to have a conversation. Sai Tai Sai refers to Goku as the 'Child of the Earth' and asks him cryptic questions such as if the world he's actually in is a dream and who he is. He also says Goku is the earth's will itself.