Tsugumi really reminded Ib of Garry best friend at first so she was a bit quicker to trust her than she normally would have been.

She likes having a sister. Since she's an only child it took some getting used to but it's nice having someone there! and even though she's the little sister here, Ib feels like she should protect Tsugumi from monsters and disappearing. It's really sad and scary that so many people have disappeared so don't do that and she'll try not to either.