The manga focuses on the hero who defeats the Demon King but is sent to Earth afterwards with his memories still intact.
He becomes the usual salary man and dies, returning to the world he left after a hundred years and meets his former companion and she hasn't aged at all. He meets some slave girl and makes her stronger and an arachnid variant girl and they go on a journey to see the world he saved.
Are you perhaps looking for Jichou shinai Motoyuusha no Tsuyokute Tanoshii New Game?
Blockquote Hit by a truck and reincarnated in a different world, then a beautiful woman greets me "Long time no see Master" Restart in Easy mode from level 1 in the peaceful world that I once saved! Follow the world's strongest sage maid, train slave girl to be strong, convert thief girl, get more friends! Even the luxurious residence and the strongest equipment remain as you wish! Be the most powerful in this new game!
Several portions of this story fits. Protagonist returns to the world he saved. Meets his former companion. Meets a slave girl and there is also an arachnid girl who joins his party.
