In the controversial Melvin Burgess novel Lady: My Life as a Bitch, a 17-year-old girl is magically transformed into a dog by a mysterious beggar. After spending much of the book trying to recapture her human form, she suddenly realises that she prefers canine life – the simple pleasure of running with the pack, eating and shagging, and not worrying about her weight or fashion or relationships. Shagging and eating and freedom.

I think that fantasy is at the heart of Tokyo Jungle, an interesting score attack game from Sony Japan and indie studio Crispy’s, set in a post-apocalyptic version of the Japanese capital. Here, the humans are gone and the streets are ruled by emancipated pets and escaped zoo animals. The player selects a beast, opting for a grazer or a hunter, and then patrols the streets, looking for food. For hunters, this means stalking and attacking smaller critters; for the herbivores it’s all about looking for tasty plants. Both lifestyles have their pros and cons, but most red-blooded gamers will want to start as a meat-eater – even if the only one open at the beginning of the game is a Pomeranian, which looks about as tough and feral as Justin Bieber in a nightie.

You begin on the tough streets of Shibuya, with great tufts of grass protruding from cracked roads and disintegrating buildings housing only chimpanzees and ravens. Hunting involves creeping up on your prey and hitting the right shoulder button to leap and rip out its neck. Eating keeps your hunger meter up, which in turn regenerates the life gauge – both will drop after lengthy periods with no food.

But it’s not all about roaming and eating. There are also territorial flags around each area – mark four of them with your scent and you get to use the local lair, a hangout where you can sleep, save the game or… shag. Yes, mating is a key element. Once you own a territory you can look for partners which come in three politically incorrect flavours: prime, average and desperate. I’m not kidding, ‘desperate’ is a category – and astonishingly, there are even bitches with fleas who’ll pass on the itchy contagion, forcing you to seek out water to bathe in – is this the first video game allegory for safe sex? Well, at least it’s the first involving escaped pets in a disintegrating city. Any how, The better your lady friend, the better the genes you pass on to your brood. And this is important because after shagging, you control the resulting puppy and its brothers, wandering the streets as a pack, able to attack in unison.

Throughout the game there are challenges to unlock, as well as power-ups and presents. You can even collect little outfits for your beasties, so you may end up patrolling the darkened streets of the deserted city wearing a ra-ra skirt and baseball cap. Only Japanese developers could force upon us such a madly dichotomous vision.

And from here on, Tokyo Jungle is like life – you survive for as long as you can, mating to ensure your lineage and guiding each successive generation through the daily challenge of existence. At times you’ll panic because your hunger meter is dropping and there are no smaller animals in your area; at other moments you’ll track your prey into a pack of wolves, capable of tearing your furry body to pieces; for a second, you get the stalling panic that perhaps prey really do experience, and then chaos. Because that’s it, little doggy, if you’re attacked and killed, it’s game over. That’s what score attack games have always been about really, the struggle to stay alive, pitted against the inevitability of demise. But here it’s with Pomeranians rather than spacecraft and it makes it all much more visceral, more primal.

And then, as you unlock more animals, you move up the food chain, eventually inhabiting ever more outlandish beasts including dinosaurs – and other breeds are available to buy as DLC. The structure is limited, but there’s plenty to explore, and lots of enjoyment to be had, building your feral empires in the wreckage of the world’s most advanced city. Really, it is an essential download, if only for curiosity value, if only to witness for yourself, the starkly authentic ruins swarming with bears and crocodiles.

But in the end, you will discover the story is always the same – life at its most pure, stripped of everything else. Shagging and eating.