Date is an EsperThe Zero Escape series has involved Mental Time Travel, especially with Virtue's Last Reward and Zero Time Dilemma as prime examples of what an Esper can do. The reason Date remembers what happened in each route leading up to the Resolution route is cause he jumped back and forth between each one.
Hitomi has a mechanical arm wrapped in ABT in the epilogueVirtue's Last Reward establishes the existence of mechanical arms and nerves as well as ABT, artificial skin that looks almost identical to the real deal, down to pores. Since Hitomi's moving her arm in the final dance sequence, this could actually be a hint she got it replaced to surprise Date.
Pewter wanted to kill DateHe deliberately gave him Aiba instead of normal prosthetic eye to drive him insane and break him.