So we often see mc transmigrated into a another world/novel, sometimes they're also accompanied by system. Aaaaand I was thinking if there is any danmei where there are also other characters who transmigrated/have system & might as well helping or clashing with MC... Found similar trope in "Looks Like I Fell Into Harem Game" (not bl), "As Minor Gay Rival in Hets Novel", "My Husband is Suffered from Terminal Illness".
The End of The World’s Reborn Cannon Fodder Counter-attacks Mc is reincarnated(I think multiple Reincarnated, idr) , there is a guy with a system, transmigrated girl (mc's world was a book she read). Probably more but I still have a lot to read.