They brought up the 10 years thing again from the time travel portion and the time traveler master that came back looked similar to this one. Haru even thought he'd be dead in 10 years. Since he's able to talk in the apocalypse, he was finally able to apologize for leaving his master behind (subverted as a joke when it turns out he lived and is still lively in the future apocalypse)
I'm not sure whether it's a dream (butterflies) or some sort of purgatory or punishment like she assumes but Haru having a child that would continue to go on adventures with his master is a pretty sweet gesture. Even in the apocalypse where he's still alive in the future, he wanted to make sure that his master won't be alone.
Although if it's a dream, it also means Haru dreamt of having a dog harem where multiple females are after him (violent tsundere white shiba as main girl, childhood friend black shiba, kouhai Corgi and a kuudere Collie) 🤣