Columbina going from indifferent to the suffering of others to the proud protector of the people of Nod Krai is truly one of the best examples of character development in Genshin.

When the Traveler first meets Columbina, she’s presented as an antisocial and reclusive loner who couldn’t care less about others and would prefer to be left alone and not engage with other people’s problems. She also had a purely transactional and cynical view of relationships, which she believed were based on self-interest  and were the only real kind of human connection. This kind of behaviour stemmed from the treatment the Frostmoon Scions and Fatui gave her, which ironically aligned with Dottore’s philosophy of people using each other for their own benefit and words like “love” and “family” are merely excuses and don’t really mean anything beyond that.

After the Traveler shows her unconditional kindness and comes to realize people like Lauma and Sandrone see her as a person instead of someone to be taken advantage from, as well as confronting Dainsleif about his personal demons and some self reflection, Columbina starts to become less cynical ,more idealistic and proactive, and during Moon Prayer Night Alrecchino notices that Columbina never really showed much consideration for others back when she was in the Fatui compared to now.

In the newest Archon Quest we finally see the culmination of her development: Columbina is now much more proactive as she extends her kindness to even former enemies like Rerir, chooses to infuse her body into Nod-Krai as kuuvahki in part to protect the land and elaborates a complex scheme to be reborn with the help of her friends, cementing herself as the ultimate protector of Nod Krai.

Her change from somebody who saw Teyvat as a hollow world full of falsehoods and couldn’t care less about others to someone who would give her all to protect Nod Krai and her friends is truly one of the greatest examples of character development in the game.
Rewatching some scenes from the beginning of the Nod Krai Archon Quest, it’s amazing how much Columbina has changed