dialog.kv

<CutsceneText@ModalView>:
    size: root.size
    current_text: 'Current Text'

    Label:
        text: root.current_text


<Conversation@BoxLayout>:
    current_name: 'Character Name'
    current_text: 'Current Dialog'

    # using __self__ so that we can add/remove these widgets at will
    current_name_widget: actor_name.__self__
    current_text_widget: dialog.__self__

    # override for target actor name
    current_name_override: None

    orientation: 'vertical'

    Button:
        id: actor_name
        halign: 'justify'
        size_hint_y: 0.2
        text: root.current_name_override if root.current_name_override is not None else root.current_name

    Button:
        id: dialog
        padding: [5, 5]
        halign: 'justify'
        valign: 'top'
        text: root.current_text


<ConversationContainer@ModalView>:
    conversation: conversation
    size: root.size

    GridLayout:
        rows: 2
        orientation: 'vertical'
        padding: [5, 5]

        BoxLayout:
            size_hint_y: 0.7

        Conversation:
            id: conversation
            size_hint_y: 0.3