Why is ちゃう used in this sentence?

Question

The character is meeting his friend's boyfriend and says this

どんな子か気になっていたけれど、かおりの事本当に大好きなんだね

Then he also thinks

守っちゃって可愛い

My reading would be "his protectiveness (of her) is cute. But why is ちゃう used here?

Answer 1

If you understand ちゃう (てしまう) only as "regrettably", this sentence might indeed seem strange. However, ちゃう is a word widely used in contexts where one does something that differs from the initial expectation or plan, or in contexts where one does something decisively. In your sentence, ちゃう indicates that the action of 守る seemed unexpected to him.

See also:

• What is the meaning of てあげられちゃうんだけど
• What are these forms: かけちゃお, つないじゃお?
• Why is ちゃった used here?

Answer 2

In terms of meaning, ちゃう/てしまう is just 完了. There are just a variety of feelings added, totally depending on the context.

The one in question is the feeling that an adult feels when seeing some actions of child. In a mild sense, the speaker is making fun of it, but not to ridicule. For examples:

• 大人ぶっちゃって - Oh you are acting like a mature person
• 着飾っちゃって - Hey you have been dressed up

I don't understand the context well, but it expresses basically the speaker finds the action of the boy's protecting かおり kind of funny (maybe not the right word). Or to an extent, using ちゃって expresses already the speaker finds it cute (i.e., the boy acting like a man is funny/cute to the speaker).