You could surely do something like that using Tie::Hash, but why not using a lookup function?

my $hash = 
{ 
    a1 => 
    { 
        a2 => 'Hi' 
    } 
};

my @key = qw {a1 a2};

print "Hash-value is ", lookup($hash, @key), "\n";

sub lookup
{
    my $hash = shift;
    my $key  = shift;
    
    return @_ ? lookup($hash->{$key}, @_) : $hash->{$key};
}
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