So... how do I use these things? I can't figure it out. I'm seeing shinki I'm fighting do a lot of maneuvers now...

Second option on the equip screen. Those skills are called "Rail Actions".

You can assign one for every direction (up, down, left, right)

To activate it, press desired direction with Triangle and Circle.

little while after posting I found that, but... I'm still having trouble getting them to work.

Sorry if either I post this too late nor too helpful.

There are three types of rail action

Movement : Usually typed MOVE : ROUTE 1-15 (I only found till 15)
These are RA so your shinki move in a preset movement. These don't have any restrictions, can be used anywhere (as long you have enough SA). If I'm not mistaken, you start with two of them. Can be used for quick retreat, quick approach, or positioning. Note that you can stop in the middle of the route and don't need to stop at the route destination by pressing an attack button.

Attack : Usually typed ATK : Weapon type
These are attacking RAs. In order to use these RA, you need specific weapon with specific RA. For Example, to use RA for knuckles, you need to equip at least a knuckle. If you equip two or more, the shinki will automatically choose the strongest of that type. Each weapon have their own specific RA, and after quite a while, there are RAs for weapon combination.

There are also some special weapon RA though. Like Big sword "Issen" move or Knuckle "Shinking Knuckle" though I dunno how to get them...

Shinki Special RA
These RA are specific to shinki and you must use their specific equipment. You can say that these are the shinki Ultimate attack.

Quick way to see if your shinki will do RA or not is after you press a direction and triangle+circle, there will be a sound and your shinki will squat(?) for a sec.

Ah, sorry for too much explanation.

Also, useful to know, depending on the weapon used, you may have a shield going on during the rail action.

Gatling and bigass swords, for exemple, usually get a strong shielf during the attack.

Ah, Thank you for reminding me, Shikaze.

Though there are differences from Super Guard and Super Armor

Big Sword and Axe RA give Super Guard. It automatically guard all attack, but the guard can be broken with enough hits (Sub Machine Gun, Bits) or Strong enough attack (can guard against bazooka, but never win against a hammer. Avoid air mines at all cost!).

Hammer, Gatling Gun and Particle Canon (The one shoot pillar) give Super Armor. All damage received is reduced (though not as big as Super Guard) and nothing will stagger you. Note though if you get hit from behind, it will nullify your super armor.

Super Armor is fixed while Super Guard can be enhanced (or reduced ) by your shinki if your shinki have good def and good defensive skills (or bad def and minus defensive skills ).

For example, my Rin (Yda) with her big sword only can stand one or two hits from ranged and only can stand one hit from melee attack before her super guard broken. On the other hand...
My Erica (Altlene) can plow trough anything with her big sword. I've seen her super guard resist more than two bazooka, hand gun and Sub Machine gun and can resist at least two hit from melee (even a hammer Though she usually lose to it at the third hit).

There are three types of guard effects, but only the first two come with the RAs.

~Shot Guard - Nulls stagger from gun-based weapons.
~Super Armor - Nulls stagger for a specific duration/number of hits.
~Guard Point - Nulls stagger for a brief period (usually upon initiation of an attack from a great sword/spear)

There are also ones used by the more noteworthy NPCs. You get these skills by unlocking achievement titles in the game.
*Hazuki Takehime: Advancing Flash (required DLC Gyurinos sword in first game, but can now work with all great swords)
*Chitose Kobayakawa: T-ARMS(works with all gatling guns)
*Gaia: Evil Howl (required DLC Suffering Goddess launcher in first game, but now works with all launchers)
CHIKARA (mk2 exclusive, works with all launchers)

At the moment there's no legit way of getting Shining Knuckle. The skill was unlocked by hackers and spread all around via Ad-Hoc battling.

I got mine through a Friend Card of someone I fought with via Ad-Hoc Party, who most probably sourced it from a hacker's FC.

Ah, about that achievement to get the special skill....How to get it?

I already fight all those three for more than 50 times and I still don't get the skill. Or there are other, different way?

Fighting them won't get you anything.

I don't have the exact names of the titles translated yet, but there's a big catch to getting Advancing Flash if you didn't carry it over from the first game: You need to win both of the handicap battles for Ach's Love Events, since they grant two of the required titles. (Symbol Of Persistence and Symbol of Perseverance)

Reset and Re-do Ach storyline, win in two handicap battle, still no advance flash.

For your information, I better tell you the progress of my save so you can pinpoint which title/battle I missed.

I finish all the love event for Arnval, Ach, Altlene, Altine, Yda, Tsugaru, Eukrante, Ianeira and JillRivers.

I haven't finish the love event for Strarf, Fubuki, Zelnogard, Howling, Maochao and Estoril.

The handicap battle that I remember is two in Ach and one in Altlene love event. There are two in Strarf storyline, but I guess those two you are supposed to lose since no matter how powerful my Strarf, that dang opponent Strarf don't lose a tiny bit of HP at all.

Is there any handicap/normal battle I missed? or there are something else missing?