Not In Vain Together

Only person that cares about Aoi is his sister, given he has no friends nor parents. That soon changes when Aoi tries to take his own life but meets someone thinking about doing the same. Not having anything else to live for, they make a promise that one of them can not kill themselves while the other one is still alive. Together they try to make each other as happy as they can while their bond grows each day that goes by.