The party finishes a hard day of travel or dungeon crawling and finds a safe spot for a long rest, they light a fire and pull out rations as the GM asks "does anyone talk around the campfire?" The players around the table shrug or shake their heads. 20 sessions later the Fighter dies in battle; everyone agrees it's sad, but they feel bad for the Fighter's player and any unresolved plot threads. None of their characters have any reason to grieve, because none of them really knew the Fighter, despite spending weeks or months wandering a hostile world together.
Players who see the emotional connections between the characters in Critical Role might wonder what's going wrong in their games. Are they bad roleplayers? Are the Critical Role players scripting out their relationships beforehand? No to both, of course. Even people who have seen complex relationships develop in narrative games such as Monsterhearts may be missing that from their D&D or Blades in the Dark games.
Make Space
The party finishes a hard day of travel or dungeon crawling and finds a safe spot for a long rest, they light a fire and pull out rations as the GM asks "does anyone talk around the campfire?" One of the players says, "I sidle over to the Wizard and ask them about..." Two PCs make a connection – possibly about how close that fireball landed in the last fight. The Fighter pipes in with a joke about how the fireball wouldn't have landed so close if the Rogue wasn't always skulking around in the back lines.
It's shallow, but it's a start. One conversation flows naturally into the next, and while initial chats may be about combat strategy, as the scope of your story expands and your players become more comfortable in their relationships with each other, they'll get to bigger topics.
As a GM, you can encourage these conversations with leading questions. "Rogue, did you notice how close that fireball landed?" "Bard, have you started composing a song about this adventure?" Keep it shallow, to begin with. Let your players get comfortable talking in-character with each other.
Make Connections
The party finishes a hard day of travel or dungeon crawling and finds a safe spot for a long rest, they light a fire and pull out rations as the GM asks "does anyone talk around the campfire?" The Bard turns to the Wizard and says, "I can't believe you sided with the Princess over us at the council."
Now we're getting somewhere. The PCs are connected to the world and they're using their connections to the world to complicate their connections to each other. When the conversation ends their relationship will never be the same.
We encourage these conversations by forming connections between the PCs and the world around them. It's tempting as a GM to look for a party consensus in big, campaign-affecting decisions, but the Bard would never have had reason to engage with the Wizard had the GM not had the Princess ask each PC, in turn, whether they agreed with her.
But not every connection needs to be world-altering. A chance encounter with a scoundrel in a tavern might hint at the Cleric's unsavory past, which leads to a game of conversational cat-and-mouse as the Rogue tries to uncover their secrets. An old mercenary comrade of the Fighter could be a childhood rival of the Paladin – what happened between them that led the NPC into the rough life of a mercenary, and whose side will the Fighter take if it comes to blows?
By making space in between action scenes we get the players comfortable talking to each other, by forming connections between PCs and the world we deepen those conversations, and with little moments and side stories we plant the seeds that grow into deep relationships.