tabletop-companion/app/views/counters/_form.html.erb

<section class="inset">
  <%= form_with model: @counter, url: character_sheet_section_counters_path(@section) do |f| %>
    <% if @counter.new_record? %>
      <%= f.fields_for :character_sheet_feature do |ff| %>
        <%= ff.hidden_field :featurable_id, value: @counter.id %>
        <%= ff.hidden_field :character_sheet_section_id, value: @section.id %>
      <% end %>
    <% end %>

    <%= f.label :name %>
    <%= f.text_field :name %>
    <%= display_form_errors(@section, :name) %>

    <%= f.submit button_text %>
  <% end %>
</section>