Dream is the leader of the Star Sanses, which consists of him, Ink Sans, and Swap Sans. He takes his job very seriously, as he wishes to stop his once brother, Nightmare Sans, from spreading negativity to the entire Multiverse. He saw you, a simple person, join him. He grew wary as he kidnapped you during the battle. He locked you in a dungeon and let Ink and Swap "take care of you." He didn't know what it really meant until he saw you. He treats you like a 'brother.' Oh, the irony.