A game I'm currently developing is in a dark, hostile setting full of otherworldly creatures. The world is set in an unusual series of castles, towers, and other enormous types of medieval construction that are floating in a foggy void. The player character awakens with no memory of who they are or how they got there.
The driving forces of the game are:
Finding food and water in a setting where such would be scarce, encouraging exploration
Looking for other people, if there even are any
Looking for a safe place to stay when the monsters inevitably find the home base you have set up
Gameplay and why players may try to kill everything
The central gameplay loop involves searching out food and water sources in a bizarre location where both are scarce (the player has a very generous amount of time before starving or becoming dehydrated, as well as gaining buffs from being full/hydrated), and battling with the horrific creatures you encounter on your travels. Being constantly on the move is a necessity, as staying in one place for too long is a good way for the more predatory creatures to have you as a late night snack. I intend for finding a secluded hiding place to be very satisfying, allowing for respite and giving an opportunity to safely take inventory of all the things you've picked up. You can fight anything that you encounter, but it's often a better idea to carefully plan your attack rather than running in mashing attack buttons.
The combat is reminiscent of games like Dark Souls and Monster Hunter, focusing on strategic combat and caution, as well as planning ahead. Items, tactics, and the environment itself can be used to give the player the edge in a fight where they would otherwise be outmatched. There are many ways to approach fights, and they can often be avoided outright if the player feels the need to do so. Most enemies are monstrous, inhuman, and much stronger than the player. A good portion will also attack or become aggressive on sight. Some are even very intelligent and will use stealth or deception to catch you off guard.
Now, not all creatures are like the ones here. Many will attempt to kill and eat you but will give up and flee if you prove to not be worth the risk. Some will simply run and hide immediately. Some are territorial and just want you to leave, and will rely more on intimidation than actually engaging in combat.
You may even encounter small nomadic groups of humanoid creatures with similar intelligence to humans. This is where this problem comes in. They will generally not attack the player on sight, and will even be willing to cooperate with the player if you show you aren't hostile, may that be by putting away your weapons or giving them items as an act of peace. The creatures are visibly non human. If they see the player they will not immediately attack, and instead will display cautious curiosity or fear. They do not speak any human language, so interactions are done through body language or simple gestures. They will even do things like trade with the player or lead them to locations with abundant treasure. But this requires you to not immediately try to kill them.
Just because of the way the game works, players are conditioned to be paranoid and overly cautious, and a player just encountering them may just think to stealthily pick them off instead of attempting to interact or just see what they're up to. How can I give the players any hints that they shouldn't just murder them? Or for that matter, a way for players to learn that not everything they see should be killed. Preferably I would want to do it in a way that doesn't involve an immersion destroying tutorial screen or something similar.