Once you are able to join the Fighter's Guild and you get Jack's Room in Radiata Town, notice a pair of red boots. They resemble the "Santa Boots" from the Star Ocean series.

Notice Gantz's appearance during events that feature him throughout the game. His outfit will begin to resemble that of Claude from Star Ocean 2 during the intermission sequences.

Once you are able to roam around the castle again after Ridley has joined the fairy creatures, go to her room. There will be a ghost on her bed. If you go to the ghost, you will wake up in your bed back under the bridge wearing Claude's uniform from Star Ocean: Till The End Of Time. It gives you HP regeneration.