While Astarion's romance is in need of some love throughout act II and III, I'll solely focus on the ending for unascended Astarion.
After defeating the Netherbrain, we end up on the docks with our companions.
Astarion: 'I - I can't feel the tadpole. It's gone - we're free! And I'm still standing in the sun. This is incredible! Maybe whatever it changed in me was permanent?' This is the first thing Astarion says while looking happy and hopeful.
And then he has to flee the sun in a way I can only describe as cruel. We (the player) spent hours and hours to bond with this character, deal with his problems, defeat Cazador, help him realize, he's a person, he's loved (dearly by a lot of us). Only to have his and our hopes crushed. I honestly can't understand, how anyone could think, it'd be a good idea to have him scurry away like that.
We're not even given a chance to react. Why can't my Char take care of the love of her life?
Now let's see what the companions have to say:
Shadowheart: It seems that's the end of Astarion's love affair with the sun. That'll be hard on him. Gale: I suppose that's the last time any of us will see him, and the last time he'll ever see the sun. Wyll: Astarion will keep to the dark now, I wager. At least... he'll find plenty to feast on. Halsin: He will sorely miss that freedom, I sense. It may be quite some time before we see him again. Jaheira: I doubt we'll ever see that face baskin in the sun again. Minsc: We will find you, Astarion! AND BOO WILL BRING A SUNFLOWER! Karlach: Didn't speak up no matter how many times I reloaded the scene.
Aside from maybe Shadowheart's, none of those remarks are acceptable. I would have punched each and everyone for it before bolting after Astarion. Instead I am forced to deal with Karlach. I am sorry but in that moment I couldn't have cared less about her fate. (Which is a shame because I really liked her up to that point.)
Why not instead have the celebration they talk about? (Dragon Age Inquisition nailed that, you get to speak with all your companions and then retreat with your LI.) ______________________________
The Epilogue for Astarion and his romantic partner is severely lacking emotional depth and intimacy. During the whole scene the PC stands there, sometimes even with crossed arms. What are those poses and facial expressions? It looks like they barely want to be in the same room. Astarion and the PC are in love, yet it's not shown at all.
Astarion: 'Hello darling. I was just thinking about freedom. How I'm free of the parasite - free of Cazador. How I'll never be in someone's power again. And all it cost was my life in the sun. Now I belong to the shadows. So. What happens next?' I like that part aside from 'What happens next?'. I'd prefer 'What are we going to do next?'.
(I'm going to only talk about one of the possible answers here since that's the one I always choose.)
PC: 'I'll help you find a way to walk in the sun again.' That line sounds incredibly condescending to me. They are in a relashionship as equals after all. Better were something along the lines of 'We could search for a way for you to walk in the sun again, love. Would you like that?'
Astarion: 'You - do you think it's possible? I suppose there is a chance. And if there's a chance, no matter how small, I'm going to take it. And it would mean setting off on another adventure together. Is that what you want? Is this what you want?' I actually really like that part as is.
Astarion: 'I would understand if you wanted to go your own way.' I think, it makes not much sense but don't really mind it being there.
PC: 'No, this is what I want.' This sentence shows no emotions whatsoever, it's completely hollow and disappointing. Please, let me tell him 'I love you, Astarion. To be with you is what I want.'
Astarion: 'Good, because selfless as I am, I really did not want to let you go.' Minor change with huge impact would be: 'Good, because I love you too and selfless as I am, I really did not want to let you go.' Astarion should take PC's hands now, drawing them closer together.
Astarion: 'We are rather excellent together, you know. And united, there is nothing we can't do. I can't say what the future holds for us, but I know we'll be facing it together.' Why don't they kiss?
Astarion: 'And we're going to have a lot of fun.' Here they should embrace each other in a tight hug before it fades to black.
- the happier end (imho) ______________________________
PS: English isn't my first language, please excuse mistakes I may have made. Better yet, let me know about them. Thanks!
