Free Characters
Etheria: Restart provides you a few characters for free that will make your early game easier - below you will find a list of every free character and how to get them!
Gray
Gray is one of the starter characters that you will have from the get-go on your account. He's a DPS/Buffer hybrid who is able to provide the whole team with valuable CRIT Rate buff (+30%!) while not really losing on doing damage. That's because whenever he uses his S2 skill to buff his allies, he also gains extra action, allowing him to act immediately and use his other skills - which usually will be his S3 that deals damage to all enemies with a chance to inflict DEF- on them, reducing their DEF stat by whopping 60%!
Gray is definitely worth investing into and keeping on your team as you will use him in a lot of PVE content.
How to obtain Gray? Prologue.
Sybil
Sybil is one of the starter characters that you will have from the get-go on your account. She's a DPS who can buff her own SPD, allowing her to act more and who can also reduce inflict DEF- on a single enemy. Compared to Gray, sadly she's purely single-target oriented and a bit of a selfish character.
Don't invest too much into Sybil, as you will quickly replace her (hell, even the game wants you to replace her with 
How to obtain Sybil? Prologue.
Cachi
Cachi is one of the starter characters that you will have from the get-go on your account. He's a buffer/debuffer Hybrid who helps allies by buffing their ATK and increasing their Turn Meter by 100%, basically allowing them act immediately - and on top of that, he can reduce the cooldown of the character skills by 1 turn. When it comes to his debuffer side, he can decrease enemy Turn Meter with both his S1 and S3 skills and also Stun them using the latter!
While Cachi is a pretty decent support for his low rarity, you won't really use him that much outside of early campaign - as there's a lot character that simply do more than him. So don't really invest into him that much.
How to obtain Cachi? Prologue.
Dorothy
Dorothy is one of the starter characters that you will obtain during the Prologue after defeating a mini-boss. She's a healer who can heal a single ally with her S1 or S2 and heal the whole party with her S3, making her quite versatile as she can adjust to every situation easily. On top of heals, she can also remove debuffs from allies which is pretty important as they are used often by enemies to hinder your party. Oh, and her S2 also applies a Healing over Time effect that triggers at the start of that ally turn, healing them or converting the heal into a shield if they're at full HP.
Dorothy is a capable healer that will fulfill all your needs in the early and middle game, but later on she will be replaced by healers that can do more than heal.
How to obtain Dorothy? Prologue.
Lian
Lian is the character you will obtain from doing the first summon - everyone gets her! She's a great damage dealer, specializing in dealing with bigger groups of enemies, who can keep herself alive with self-healing and steal the enemy Turn Meter, disrupting their pace. Both her S1 and S2 scale with the amount of buffs Lian has on herself, making it very important to pair her with characters that can provide buffs to her.
Lian will carry you through the early and mid game and still will have a lot uses in the endgame in various PVE content, so it's worth investing into her. What's more, there are several missions that provide you with additional resources for hitting certain milestones in Lian, so it's worth doing anyway!
How to obtain Lian? Tutorial Summon.
Lingluo
Lingluo you will be able to obtain from the 7 Day Commission event, but it will take you a week to do all the missions needed to get her. She's one of the best healers in the game, so the fact that she's free is pretty wild! Not only she can heal allies with all her skills, but on top of that she can remove debuffs and extend the buff duration on them. Furthermore, she can grant Immunity to allies, preventing them from getting any debuffs! Her healing scales with allies HP and the amount of buffs that are present on them.
How to obtain Lingluo? 7 Day Commission event.
Here's the event screen where you can obtain her:
Targeted Summon
On top of the characters listed above, you will be able to obtain any* RGB SSR character from the Targeted Summon banner. Here's how it works - pick who you want and you will get them within 40 pulls. Simple!
Any* - 