Defeat Suzaku Leader. She will tell you a little about it. Talk to girl in Phoenix Bay. She will tell you to go to Bios Swamp. This is right from the Bulk Bridge area. Find the Shrine and you will find Crest of Sincerity (sic, as appears in the game) then you will think about asking Sepikmon. Go to see Sepikmon. He suggests seeing Baronmon about a bomb. Go to Tyranno Valley. Defeat some Triceramon until you get a TNT Ball. Take the TNT Ball to Baronmon in Protocol Ruins. He will make a TNT Chip. Go all the way back to Shrine and blow up the wall. In the Shrine, climb down the ladder to find the Digi-Egg Of Reliability. Note that your character calls it the Digi-Egg Of Sincerity.