"You promise?" she whispered. Her other problems would be left unvoiced and to fester inside her heart until it became too heavy for her to shoulder alone. Whatever fears Zero Two was having inside her heart right now, he would be there to immediately ease them away. That's what he swore to do. "I promise." (AO3/FF)

In the distant future after the destruction of VIRM, not all goes to plan when Hiro and Zero Two get reincarnated. AU continuing after the series ended.

Jin is a veteran parasite who, after many years of service to humanity has honed and perfected his abilities to a level like none other, standing atop all other parasites, and arguably, even the nines; however, not everyone is born strong, some must to fight to become strong. "Out of suffering have emerged the strongest souls; the most massive characters are seared with scars."