The main draw of the Domaru Butai's offensive capabilities is how focused on being a unit that excels in close combat. At CC 23, Domaru is quite a monster compared to most units.He also sports Martial Arts Level 3, Berserk, and Dual Wield to compliment his CC 23 as well. Being that he is at PH 14 as well, he is going to cut through most units with ease in Melee. The most common CC weapon loadout on Domaru Butai is both the Shock and E/M CC weapon, which means most 1 wound models will go straight to dead and HIs and TAGs will become immobilized and isolated. One thing to keep in mind is that if you use Dual wield, the critical hit occurs for the E/M CC Weapon but not the Shock CC Weapon.
At BS 12, the Domaru Butai tend to be a little underwhelming compared to most heavy infantry. On most profiles, it is not going to matter that much due to their main weapon being a Chain rifle. The Spitfire Domaru is certainly a good medium-range option, but to get the maximum effect she needs to be in a link team. If needed, their E/M grenades can be used to great effect in dealing with link teams if they are close by.
Having ARM and BTS 3, the Domaru are relatively average in terms of defensive stats. While Domaru can survive a few hacking attacks, most hackers will eventually get through and put the Domaru in a bad position. However, due to Martial Arts, Domaru can use stealth to get around hackers without Sixth Sense and their repeaters. With access to V: Courage due to Martial Arts LV 3, the Domaru are going to pick and choose most of their battles and voluntarily ignore retreat in certain situations.
One of the things that makes them great defensively is the use of Chain Rifle when someone gets close to them. This forces them to either dodge or it takes an unopposed shot with a guaranteed hit. The downside is your opponent gets a normal roll on his shot, but it can cost them their own model.
+Hacking is a problem for Domaru in the reactive turn. However, you can use stealth to deny the opponent's chance to use a hacking ARO in their reactive turn. However, this does not work if they have the sixth sense skill at any level.
+E/M Grenades and chain rifle in the reactive turn can threaten models who decide to get close to you. While it does leave the Domaru open to a normal roll, but it means that the attacking model is forced to make saves as well. With this being in a link team as well, it can be a risky proposition to most units if they do not get a wound on the Domaru or put them in the unconscious state.
+If you are deciding to use Dual-Wield, one thing to keep in mind is how criticals effect what effect happens automatically due to rolling the critical. With the baseline Domaru with E/M and Shock CC, E/M would be the automatic effect but the Shock effect of dual wield still needs to make an armor save. Which means anyone that survives the critical still suffers the effect of E/M.
With the Domaru being Heavy Infantry, hacking is one of the ways to stop them. Keep in mind though that the Stealth from Martial Arts means in the active turn they are harder to hack, so this is more reserved when they are in the active turn. One thing to look out for is Fairy Dust, which can make the Domaru harder to hack but is still manageable. In that case, an Assault Hacker is your best choice.
In the case of firefights, the Domaru are weak at longer ranges. The longest range weapon they have is the Spitfire, in which loses its effectiveness in the reactive turn. If you are forced to get into close range, it might be preferable to exchange template fire against them for an even trade or having Natural Born Warrior to negate Martial arts in CC.
Despite being on the cheaper end for Heavy Infantry, most lists including them are going to keep them at one or two if you are not playing with one combat group. With a Duo, you can have a relatively cheap link team for order efficiency and escorting the specialist Domaru to the objective. Where the Domaru shine though is forming into a core fire team.
When it comes to forming the Domaru core link, the rule of thumb is to take at least two Tankos. Not only can you make the link team cheaper with some options, but give you an option for the Missile Launcher for longer range engagements, mostly for the reactive turn. It can be possible to to add a spitfire Domaru into the mix, but this starts to become a very SWC intensive link team. However, this does give you a well-rounded link team. If you are planning to go with a 'Samurai/DoTanko' link team as it is dubbed, it may be wise to consider the impact it will have on your order economy (odds are you will end up with a single combat group.)
When looking at Haris options for the Domaru, there is a vast array of options. Starting with the vanilla Domaru Haris, you can take the Haris option with two baseline troops as your basis. While it does give you order efficiency, it is very short range and has no punch. For a better loadout, take the Haris option, Spitfire and the Forward observer for about 2.5 SWC and 102 points. However, the specialist option is not necessary which can shave a few more points for another order. Looking at the Karakuri Haris, the Haris Domaru option can help to shave off up to 9 points, which can get you another Keisotsu to generate an order. The final one is the Daiyokai + 2 Domaru option, which can give the Daiyokai close range defense via the Domaru's chain rifle and E/M grenades. While this is usually the most expensive compared to the former two, it can give your Daiyokai a lot of hitting power.
Looking at Duo, it is a cheap way to create a Domaru link team for order efficiency. This said, you will miss out a lot of bonuses but you can use it to save points to use elsewhere.
Being that the Domaru is one of your non-SWC lieutenant options, more often than not he is probably going to be taken if all possible while still being at a respectable WIP 13. Make sure you have your CoC Kempeitai in your list to cover your back if you go into loss of lieutenant.
Outside the use of Flash Pulse from the forward observer, the Domaru should be deploy in full cover as much as possible. Keeping this in mind, your Domaru should deploy in a manner to start moving up towards the target. As before, use the pathway that will generate the least amount of AROs to keep them alive as much as possible. Another thing to add to this is that the Domaru can be very good with covering your flanks against impersonation and AD Troopers, either with their chain rifles or E/M grenades.
Active Turn Role
Since the Domaru are meant to be an aggressive unit, they should be getting up the board as quick as possible. Chain Rifles will be good with dealing with Camo marker units and other units with modifiers to hit them (such as ODD, Mimetism, etc). Where they shine is close combat, but requires a lot of orders to get into close combat. If you plan to, make sure you use the cover of smoke to protect your approach by one of three characters with smoke grenades in JSA (this being Yojimbo, Shinobu Kitsune and Saito Togan).
Considering the lack of low-burst, long range weapons on the Domaru you are limited on options on your reactive turn. For the most part, you are using the Domaru's chain rifle to force the opponent to take an unopposed ARM roll or waste their order dodging. This can be good for protecting your flanks with one of your Domaru against AD troopers as mentioned before. One other thing of note is using the Domaru a link team with Tankos for the maximum effect in ARO with the Tankos various loadouts. Usually you want to include the missile launcher.