I think this is the only series by hicoromo kyouichi where unlike the female protagonist who are corrupted, she is not corrupted but she made a noble sacrifice by encouraging the hero and make him live by sucking her blood but made her infected that will cause her to turn into a freak like him since he was turned into a monster like the others from previous ones due to an experiment by the evil organisation throughout the series a long time ago which means one day she will become a monster like him but regain her spirit and memory of who she is as she will soon join his side as a heroine to fight against other 'evolved humans ' like tackle from Kamen rider stronger
Hence why it was entitled 'bittersweet' not 'sweet' ,why it is black and white not colored and why it is blue because she is not corrupted
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