Minato noticing how much more comfortable Koyuki has become around him 🥹 but because of that he doesn’t want to ruin what they have already and so the chain and padlock means that he is locking away his feelings for her
Ever since Minato was young he always focused on putting other people’s feelings and needs over his own…it’s gotten to the point where he can’t truly open up and be honest about what he truly wants