Guardian Heroes is only copyrighted to SEGA. Some people thought SEGA published Treasure games (Gunstar, Alien Soldier, Light Crusader, etc) may have been co-op ownership but its SEGA only actually.
There was rumors SEGA sold REZ to Microsoft but that was false as well
Seaman also had rumors SEGA gave rights to Nintendo back in 2012 cause the creator wanted to revive it for the 3DS, but thats false as well. (also i find it strange OPeNBooK Co., Ltd is listed in copyrights but they havent used that name since the 90s. Their called Vivarium Inc now unless something happened recently?)
Also Vanillware IPs are SEGA IP's as well so as a result alot of Atlus published titles like Power Instinct, Maken X, Growlanser, etc are SEGA IPs as well.