NieR Reincarnation has launched a collaboration event with NieR Replicant. You can summon 4* versions of Kaine, Protagonist, and Emil. There are also free 3* versions that you can acquire in the event shop through Shop>Exchange with event medals. Make sure to complete all 3 difficulties of the event, titled “Record: Pure Hills”, and pick up the characters and their weapons. Equip those weapons in your loadout for a medal bonus drop. A full event guide with a lot more information can be read here. Good luck on your pulls and farming!