With Update 30, in mid June of 2021, ZOS added a new ESO Companion System. These are NPCs that will travel alongside the player and will be a companion that can tank, dps or heal.
Bastian can help any player defeat more difficult enemies and especially newer players have an opportunity to pick up bigger challenges, without having to ask others.
Also, if the group is a player short, Bastian can replace a group member. Meaning if they want to go into a 4-player dungeon and they are only 3 people, someone can summon Bastian and the group will be full.Bastian won’t be able to do complex mechanics, though, so he might not always be favored over other players.
It is also not possible to summon Bastian while in combat, but perfectly able to unsummon him while in combat.
He will also not be able to be summoned in PvP instances, in single player arenas or in housing instances.
Also, in instances where you can’t navigate to Bastian and talk to him, he will be briefly invisible, such as while swimming.
At this point in time you cannot romance Bastian.