Jinshi is the heir apparent, but has successfully stalled his appointment as Crown Prince. He wants to continue interacting with Maomao as they are, and his status as a prince being known will definitely change that. Maomao is also about to be the recognized daughter of the La clan so their statuses will be changing anyways, but he's a FUCKING PRINCE. So much baggage with the title tbh. The Emperor is THE legitimate Emperor, don't worry. The previous Emperor is a pedophile and the current Emperor's mother, Anshi, gave birth to the current Emperor when she was just 11 years old. Jinshi hates his status especially by this time he has fallen in love with Maomao as being the Crown Prince and eventually an emperor gives him too much work, and he is actually too kind to make ruthless decisions an Emperor will need to make to govern the country well. Jinshi hates sacrifices except himself so yeah.

As for Jinshi's real identity, he is the biological son of the current Emperor, Yang, and the previous Pure Consort, Ah Duo. However, as Anshi also gave birth to a son at the same time but she got something like postpartum syndrome as that son, Jinshi's biological uncle, was conceived by revenge rape on the pedophile Emperor, Anshi didn't really like her son, but she agreed with Ah Duo to swap the baby boys so as to protect the children. Eventually Jinshi's uncle died due to Fengming feeding the baby boy aconite honey (discussed in Season 1 PLEASE WATCH THE SHOW CAREFULLY). Jinshi's current identity is the Moon Prince, Ka Zuigetsu, the current Emperor's brother, but he is the current Emperor's biological son and has raised him so. Only few knew the secret, including Maomao, who deduced the whole thing.