sesshomaru's arc in my sequel idea is... learning to overcome grief and opening up again. because rin's death would have certainly affected him. he opened up to allow a mortal into his life, raised her as a daughter and watched her live a full life.

she grew up and in turn allowed herself to forgive people and let them in too. it was wonderful.

but like all mortals, she couldn't escape death forever. so in time she did pass away from old age. and sesshomaru, who had never encountered grief in this way before, never fully recovered from that loss.