First Circle Trainers are found in the Fighter's Hall in North Puddleby, and are in the first room as you enter. The skills they teach are the foundation of fighting a person needs to understand before they move on to the next circle of fighter trainers.
Atkus allows you to hit monsters more easily. It's the accuracy of each swing, and I'll use both Atkus and accuracy interchangeably throughout this guide. If you find yourself whiffing beasts at your level, then train up some atkus. It's a fast way to advance to the second circle and move up to more challenging areas, so long as you offset it with the other first circle trainers. The price for atkus' training is that as you continue to train with him, you use as bit more balance per swing. It is important to offset Atkus training with Swengus, Balthus or Regia.
Swengus is a combination trainer. He teaches a little bit of Balthus and a little bit of Regia. He's the only way a first circle fighter can increase these attributes specifically to offset Atkus training. There is no down side to training with Swengus. Some even believe he gives a little bit of a bonus over training Balthus and Regia separately.
Evus trains a little bit of almost everything. Evus is fickle about his mix of these trainings, and percentages about what he trains fly about. At once he trained less Atkus, and fighters who exclusively trained with him, found that they couldn't hit anything they didn't slaughter, and hit a wall far faster than they should have. That problem in his training has been fixed, and now he trains a bit more atkus per rank, but now the down side is that fighters who train exclusively with him will find their swing count (number of consecutive swings they can make) slowly deteriorates over time. So, it is a good idea to offset his training with a bit of Swengus or Balthus and Regia. Evus has a small bonus associated with his training, so you actually get more than 1 rank's worth of lessons when training him.
side note 1: There's a school of thought among some fighters that training straight evus is the quickest way to pass the second circle. That seemed to be true for a time, but now, with the changes in beasts and Evus it is unsure whether this is still correct.
side note 2: Many fighters choose to use Evus to increase their Histia because they believe it raises your slaughter less. Though it is not proven that the equivalent amount of histia in Evus' training raises your slaughter less than the equivalent amount of Histia Training. If anything, Evus allows them to improve their overall performance while their slaughter rises more naturally, which keeps their "wall" the same distance away.
Histia trains a fighter to be tougher to kill by increasing the amount of health (hit points) a fighter has. A fighter with a significant amount of Histia and skill can even disregard the old adage "Don't fight on Red." Some Healers complain that that with a lot of Histia it takes much longer to heal you to full health. This can be offset by training Spirtus or #Rodnus to make you easier to heal. A fighter can wait until they hit 4• to train Rodnus, then add additional Spirtus if they wish.
After passing the Second Circle Fighter Test, you get access to the Second Circle room to the east of the first circle room of the fighter hall. The trainers are as follows:
Detha is a popular trainer because she allows you to avoid taking blows by increasing your base defense. Your base defense is the amount of balance you have when your balance bar is completely depleted. Because of this some fighters have called Detha "non-portable balance" — meaning you can't use it to attack, only to defend. However, one rank of Detha give more defense than one rank of Balthus because of this limitation. Some fighters do not like Detha all that much, and prefer to train Balthus to increase their defense. Balthus and Detha make up your total defense (plus any Evus and Swengus, though those amounts are much smaller unless one has trained a lot of either of these trainers.)
side note: Detha vs. Histia Once a young Fen'neko female fighter by the name of Ananna, asked me if it was better to have a large amount of Detha or a large amount of Histia. I replied, "Well, what's better? being able to take more hits, or being able to avoid being hit?" However with the increase of some higher level monsters' atkus and lucky hits?, the detha advantage has been lessened. Currently the matter remains in debate.
Balthus is the amount of balance you have to use to attack with. The higher your balance the harder it is to hit you. The higher your balance gets the more swings you'll have, before you must rely on Regia to swing.
Regia is a complement to Balthus and governs how fast you regain your balance after each swing. Both Atkus and Darkus also add a little Balthus, so for fighters training those two trainers, it can seem like Regia is slowing down when in reality it is still at the same speed, but there is more balance to regain. With enough Regia a fighter will be able to get in one more swing, and be ready to attack again within a few seconds. With a large amount of Regia, it is possible to become capable of dealing out an infinite number of swings. There is no known down side to training high Regia.
Darkus affects how much potential damage you can do with each hit you get. The damage dealt by both exiles and monsters fluctuates, but as you train up Darkus your entire range is shifted up. If you want to be able to kill things quickly, train up Darkus until you can one hit most lesser beasts.
Darkus uses Balthus, and there is some Balthus taught along with the Darkus lessons. Thus after a significant number of lessons, balance regeneration appears to slow down because there is more balance to regain.
Third Circle Trainers do not reside in the third circle room of the training hall because they don't get along with Evus. The reason they don't get along is that for each rank you train you get the equivalent of two ranks in whatever the trainer trains, but you loose one rank of Evus. So, Evus has banned them from the fighter hall and they remain in hiding in a far off secret location. If you really want to train with one of them after obtaining 3rd circle, ask a higher level fighter for their location and put together a strong party that can reach them.
Angilsa is a female Zo Regia trainer in the trainer grotto. One rank trained with Angilsa equals two ranks of Regia minus one rank in Evus. Angilsa is a very effective way to fix a fighter who has mucked up his or her training with too much Darkus and/or Atkus and has very slow balance regeneration. As mentioned before the down side is a loss of one rank of Evus. Because of this many fighters refuse to train with her.
Knox is a Higher powered Darkus trainer in the trainer grotto. As with Angilsa, one rank of Knox equals 2 ranks of Darkus minus one rank of Evus. Knox is very effective for fighters who wish to augment their Darkus very fast, and who don't care about the penalty.
There is currently only one Fourth circle fighter trainer, by the name of Rodnus. It is unknown if another fourth circle trainer, or any above the fourth circle will come to our island chain anytime in the future.
Rodnus is a thoom located in the trainer grotto with the ability to train fourth circle fighters and above so that they can be healed faster. Because of his effectiveness, Rodnus will only train up to 50 ranks in his skill. Spirtus also contains some Rodnus, so fighters who have trained some Spirtus are unable to train Rodnus to the maximum.
Many fighters regard Rodnus as an essential trainer for more deadly hunts because of his ability to allow you to get healed more quickly. Rodnus speeds up healing by making a healer heal faster. In general, healers who base their healing on Faustus are less likely to appreciate fighters who train Rodnus than those who base their healing on Respia.
Above Fouth Circle
Atkia improves Atkus, Darkus and Swengus (which is a combination of Balthus and Regia) according to the best available information.
Aktur is a pure accuracy trainer. Training him directly will wreak havoc on your balance.