I'm going to start this game after hearing it's even better than Enicia and the contract mark.
Is it possible to get the good/true ending even if I go full corruption?
Or do I have to do a pure/no vag*nal run for it?
Anything missable here?
There are 3 actual endings in the game. One of them is a non-lewd (good) ending where you don't have to be pure but at the same time you can't be fully corrupted. Everytime you max out your indecency exp, you will be given a quest where you manually increase the lewdness level so you can just get up to level 2 and hold off on reaching level 3 if you want to do the 'good' ending.
Lafleur training progress is irrelevant to the actual ending (but there is one post game scene).
Good Ending: Can be level 1 and 2 lewdness, virginity doesn't matter afaik.
Lewd Ending (Virgin): Level 3 lewdness while maintaining virginity. (Some level 2 events removes virginity)
Lewd Ending: Level 3 lewdness and lose virginity
Not really any missables except for lafleur training where if you save her before it fully completes, you will have to wait till ng+ to see the scene. There's also a bad ending if you lose in a one time encounter in Altoce.