if you read the past mino story, the plot has certain ideas of making the MC immortal by making him also a prisoner, it requires that the MC do more actions that the contract is not supposed to do like torture or make the prisoner suffer etc.
Well, thanks to a route on the bad master, I can say that there is a hint of immortality on it. But I said both be locked since we kinda know that asterion though he might not like been inside the hotel. He truly enjoys the company and his guest. My reason to say my perfect ending is just to give ideas on the air.
But, for now, it is hard to see the Love Route to be a happy ending. Since we know, asterion said that it is small compared with the time he has been on the hotel.
Now about the Immortality, I guess is a Taboo since the bad ending show us what happens… I kinda wished to finally be back with a sense of justice, but I guess acting indifferent breaks our character.
For the age thing… It is hard to formulate around it, but I can say this will be a sad ending if MC has a normal life span, but who knows…
Anyway, I actually want a happy ending for our Asterion and MC, But I guess what we will get will be a bitter sweat ending. I have many theories and what if, scenarios but most of them are bitter, or just outright heartbreaking.