While the bacon, enoki, and scallions (green onions) make up the substance of this dish, I would argue that the tare sauce is actually the most important part to get right. To that end, I'm going to use this section to break down a few key notes about the ingredients, putting the skewers together, and how to really nail that luxuriously salty-savoury-sweet sauce.

There's enormous diversity in the character and quality of these ingredients, and learning how best to use them is an absolute game-changer when it comes to Japanese cooking. I covered these ingredients in a lot more detail in my guide to making ponzu shoyu, so if you're looking to take a deep dive into this stuff, I suggest heading there.

I highly recommend checking out the mirin Pantry Page guide here on Diversivore if you're new to using that ingredient.  Mirin is supposed to be a sweet rice wine, but the most commonly available versions outside of Japan are often little more than flavoured corn syrup.  I'm not a fan.  The good news is that you can substitute for mirin with sake plus added sugar.  Given that you're already using sake here, it's a simple swap to make.  On that note, I personally recommend using at least a moderate-quality sake to cook with.  Some consider it overkill and prefer to use the cheap stuff, but I personally take the same approach that I do with cooking wines: if I can't at least tolerate the flavour on its own, I don't want it in my food.

Shoyu (soy sauce) is a far, far more complex ingredient than many Western cooks realize.  Given that it's such a major component of the tare sauce, it's definitely something you want to look into.  At the bare minimum, I suggest using a traditionally brewed soy sauce, rather than one made using acid-hydrolysis.  Hydrolyzed soy sauces are cheap, fast, and easy to make, but they tend to taste much more brash and harsh than traditionally brewed sauces.  By law, Japanese shoyu must be at least partially traditionally brewed (some cheap versions blend in hydrolyzed soy sauce).  This means that you're making a pretty safe bet by using something like Kikkoman.

Finally, a note about salt.  Between the shoyu and the bacon, there's a lot of salt here.  If you want to cut the salt down, you can find some very good quality reduced-sodium soy sauces on the market.  Once again, look for something traditionally brewed, and trust your taste buds.  Note that 'light' soy sauce is NOT the same as 'lite' or low-sodium soy sauce.  Light soy sauce (called usukuchi shoyu in Japanese) is lighter in colour, but is actually saltier than its dark (koikuchi) cousin.  Usukuchi shoyu is great stuff, but I prefer darker, less salty varieties for making tare, as the cooking process concentrates the salt content even further.

The word 'tare' (TA-ray) deserves to be better known in the English language. Tare sauces sweetened, thickened soy sauces used for (amongst other things) dipping or basting grilled meats. These have largely been filtered into Western culinary consciousness in the form of teriyaki sauces.  I find store-bought teriyaki sauces are rarely worth using, and after you've tried making your own tare sauce, I think you'll agree that homemade tare isn't just tastier, but wonderfully easy too.

The actual instructions for making this maple-infused tare are pretty straightforward, so I won't get into much detail here.  Don't be afraid to taste test a little as you go along - you want the tare to be thick, and to have a strong (but not over-concentrated) salty/sweet kick.  If you overthicken your tare a bit, you can rescue it by adding some water, assuming you can catch it before it burns.

Tare sauce keeps well in the fridge and can even be frozen, so don't be afraid to make larger batches if you're planning to do a lot of Japanese grilling.

I find it easiest to wrap the bundles if you keep the bacon somewhat cold, as it tends to fall apart a little less.  Thin cut bacon makes this a lot easier; thick cut bacon is going to be a bit harder to work with, and it won't cling to itself as much.

Because the mushrooms and bacon don't really hold tight to the skewers, I find it easier to manipulate these on the grill if you run two skewers through each set of bundles (see above).  This keeps them from rotating on the skewers when you go to flip them, and also saves you from accidentally letting a skewer slip down into the spaces on your grill.