I got to say my first DMC game was the third one. If I'd met with Dante on 1,2 or 4 or maybe SMT, I'm pretty sure I could never love him as I do today.
So DMC3.
To be honest the whole game was a cheesy mess with some touching subplots going around to me. Up to a point at least.
The scene that started it all:
Till that point, I always thought Dante was like a slightly more quiet Deadpool or something. Always messing up, making cheesy one liners and never getting serious; but this scene, this library is like the monument of character development. Dante shows that he is not a walking funbox; but a human being in core. And not only we get to see Dante understanding and caring about everything's been going on, we get to see a broken, emotionally wasted Lady afraid to go on anymore, and a Vergil that is going further with nothing but determination to take his enemy down, to get the job done. The game introduces every character with not verbal narrative, but with an emotional one. At that point, just like Dante, I also come to understand and began to care about the whole thing, I understood everyone's motivation and they became real persons.
Anything that happened after that single moment not only complimented the game; but made me go through a even more emotional experience in my second, third and other playthroughs. Arkham explaining his motivation that was his misery, Lady killing his father with the last bits of her strength and breaking down, bursting into tears and of course the final dialogues between twins... Every single dialogue, the whole finale...
In short, the whole game wouldn't and couldn't make sense if that particular scene never happened and it could never cause such an emotional impact.
If it wasn't for that scene, DMC could never be a beloved tale in my heart. I could never feel any emotion while playing the other games and I could never love Dante as a character. But since then, whenever I hear/see/remember anything about DMC, I feel like crying. Whether they are tears of sadness or joy.