in japanese its sorta a reversed 'of'. it can also be used for applying adjectives or for showing possession of something. here "anata (you) no risou (ideal) no heroine" would translate to "heroine of ideal of you" or "your ideal heroine"
Hitoke no nai houkago no rouka no sumi odoriba wa watashi dake no butai Daremo shiranai suteeji Itsumo no yō ni hitorikiri Asemamire no keikochuu Guuzen toorikakatta anata ni deatta Hanasu tabi mune no naka Maru de higeki o miyoeta youna Kanjou ga afuredashite kuru no Shiawase ni tsutsumareru Anata no risou no hiroin Itsu no hi ni ka naremasu you ni Adoribu ga nigate na watashi o Sutekina shinario de michibiite Kurikaeshi oboeta serifu mo Kitto me o mite wa ienai kara Zutto soba de tada no kouhai o Enji sasete kudasai