All characters
Talk to Cotton with Fuse and/or Doll on your team.
Talk to the woman on the street in Shrike with Fei-on in your team.
Talk to the skeleton in Koorong with Gen on your team.
Talk to Mesarthim with different mystics on the team
Visit Lute's House with Lute in the team.
Talk to the kids in the playground in Shrike with Red or Riki as the hero.
Meet Captain Hamilton and travel to Mondo's base with Gen in your party.
Talk to Rei with White Rose in the team before going to the Dark Labyrinth.
Visit Princess Rei's Bedroom in Chateau Aiguille with Rei in your team.
Talk to the Nakajima Foreman in the Scrap Pub with Asellus as the hero.
Talk to the bunnylady who mentions the gnome with Emelia as the hero.
Travel to Tanzer and meet Nomad with Red as the hero.
Talk to all the wine brewers in Yorkland during the Arcane Quest with Red.
The start of Tanzer is different for each character. Can't remember the specifics but heroic types like Asellus, Red, and Fuse will fight the skeleton, while others won't. In addition, Red and Fuse has additional internal thoughts about Nomad.
T260
With T260G, talk with people in the arena after winning each match (including the Bar)
T260g has a unique response to the Grail Card
EMELIA
With Emelia, refuse the offer of Roufas and try to go to another region
With Emelia, right after the room with Laser, beat the 02 monsters and try to open the door before going up the stairs (an arrow will not appear on this door in the remaster version)
Emelia Grail Card conversa com vinheiros
RIKI
With Riki, do a quicksave after arriving at the Scrap Salon, and talk only with Mei Ling, after the meeting with Caballero different dialogues will appear with Lute, T260 and especially Gen
With Riki, have Annie at your party before picking up the Yorkland ring
With Riki, have humans in your party in the 2nd and 3rd position when facing King Sei, (Some humans won't say anything, Emelia for example)
LUTE
Conversa com vinheiros, Grail Card
Leve Gen para enfrentar Mondo
ASELLUS
With Asellus, go talk to Gina after meet the escape pilot in the tavern
After meeting Orlouge for the first time, try to go with Asellus to your Chamber or the place with monsters before going to RootVille with Ildon at your party
As Asellus, with White Rose in your party, talk to Gozarus at his house (or you won't be able to buy Phantasm Sword and recruit Time Lord later)
As Asellus, if you left Facinaturu via Trinity or Kurenai then at Owmi the pilot will ask how you got here.
FUSE
After completing Emelia's story, and without completing the Fuse-Emelia quest, try to recruit Emelia in Baccarat with Fuse (Arcane quest)
As Fuse, if you lose track of Emilia at Trinity Base and later do the Rune Quest, Annie's interaction is different.
As Fuse, he will have a unique interaction with the Mind magic trainer
As Fuse in a non-Blue case, recruit Blue in Devin and then attempt to travel to the Magic Kingdom. Blue's line is different than Rouge's.
Fuse has a completely different reason for getting the Shield Card and a unique line if he loses against Suzaku.
RED
I believe Doll's recruitment dialogue changes if you wait until after the palace is destroyed.
Vinheiros em Grail Card
BLUE
Blue has a unique response when Fei-On ask for help on Tanzer
Blue will have a unique interaction with the Mind magic trainer too (before the battle with Rouge)
With Blouge, go to meet Lord Virgil and Rei (the girl in Devin who sends you to Kylin's paradise) after the twin duel, winning or losing