{
  package Bar;

  use Moo;
  with "Moo::BrightChild::Role";

  sub ping_parent {
    print "Hello ", shift->controlling_parent, "!\n";
  }

  package Foo;

  use Moo;
  use MooX::TwoWayRelations;

  has_two_way bar => qw/is rw/;

}

my $bar = Bar->new;
my $foo = Foo->new( bar => $bar );

$bar->ping_parent; # greets its parent, $foo

$foo->bar( undef );

$bar->ping_parent; # is now an orphan and greets undefined.

This dist would consist of two modules

MooX::TwoWayRelations - adds the has_two_way function to set up an two-way attribute.

Moo::BrightChild::Role - a child that knows who it's parents is/are.

I'm clueless on implementation details. Thought I'd throw the idea out there (and also hear if it exists). I would not know what names to search for.