[Erwin actually smiles when Mikasa threatens to kill him. Does she genuinely think this is the first time he's heard that threat? The first time he's heard that threat from an Ackerman? He's sure that this time, it won't eventually end in getting married, but still, the irony is entertaining.]

Of course.

[His voice has gone light and cheery as she storms away.]

Because protecting him from the consequences of his actions worked out so well the last time, didn't it?