After Reincarnating, I Inherited a Honmaru

I lived a peaceful life until I died of old age. I thought that once I closed my eyes, my life would be over, but I never expected to become a sword spirit. Not a sword spirit from Touken Ranbu, but a sword spirit about to take over a honmaru. Well, retirement is retirement, no matter where I am... But what was that about stepping outside and landing in a time tunnel? Don't old men deserve a peaceful retirement? Theme: A peaceful retirement