Starlight Falling from the Distant Night Sky

I thought becoming sworn brothers with someone who had transmigrated from another world was strange enough. I never expected that after I died, I would transmigrate to my brother's world too, and even meet my second brother. But this person... is he really the second brother I know?

P.S. A fantasy setting in an alternate world, with an “if” premise. A collaborative work, with the copyright jointly owned by the coauthors.