Same guide/reference sheet for the combat:
Stats:
HP: your health, not something I would prioritize as killing someone before they kill you is better than being very tanky, as long as you keep up with chips and armors you shouldn't have to worry about it
EN: like mana, you can avoid needing too much of it by splitting your loadout between ammo and energy weapons
melee: melee damage increase
ranged: range damage increase
armor: seems to be a flat damage reduction, as such, it is important to keep your armor level on par. 10 less armor might mean going from 10 to 20 damage (double).
Mobility: speed stat, very strong
atk/def supp: what your support character provides
Weapons:
Each weapon has a few stats: Whether it is EN or ballistic and whether it is melee or ranged. EN requires energy, ballistic uses ammo, and enemies seem to have different resistances to the types, so sometimes an enemy takes a lot more from EN types. Melee/ranged affects what stat they scale off (melee or ranged). Some enemies are flying (high avoidance against melee weapons) or armored (high avoidance against ranged weapons). Unless the mission is weird, you generally want to focus on melee or ranged with a mix of EN and ballistic. This way you maximize your damage scaling off of the melee and ranged stats.
You can upgrade weapons 3 times, which you should try to do. The final time you require a special item which you can get from the black market. This is often a big upgrade, and can make the beginner weapons surpass the newer weapons until those get the 3rd upgrade. (3rd upgrade = lvl 4)
as for specific weapons:
Vamp's fang: item from the arena, very powerful since it lets you heal yourself and regen energy from attacking. So it is a full heal+EN with decent damage.
flame burner: early arena weapon. AOE weapon that also leaves a burning effect (like poison effects in other games, very powerful since it is % based damage meaning it melts bosses)
harvest moon: combined with flame burner it is very powerful since the burning efect makes this one stronger. With upgrades it lets you dump your debuffs on your opponents, which is especially great against bosses that are often resistant when you try to use debuffs.
plasma rifle: decent early-mid game weapon
tinkerbell: lategame weapon which is a bit odd, when you use it will fire rockets every attack afterwards, but if you get hit there is a chance it is gone.
regenerator 2: a secret mission reward IIRC, it both heals you at 50% as well giving you a healing buff, very useful to pop to heal yourself and get a bit of extra durability while you continue to fight.
muramase (village rain): you get this if you win the arena, insane with crit build, does more damage than a TP.
as for armor and chips: you generally want to specialize in either melee or ranged, and pick the approperiate chip+armor.
support characters:
Tira: generally the most useful, her heal lets you top yourself off while fighting, and later on her +crit chance and +crit damage lets you deal retarded levels of damage. Combine with weapons and chips that get a bonus on crit and you often fuck up bosses bad in 1 or 2 attacks (no trump attack required).
Lunya: Her active abilities are not too interesting, but her passive heal after every battle victory makes her amazing at farming. She also gives the highest +attack which I prefer over defense.
kukori: Not really my style. She gives you defense rather than offense. I like her 9 turn regen and ability to remove flying+armored+slow down enemies. Her passive abilities either let you enjoy +25% stats, or hit really hard with your trump power, but her lack of attack stat counteracts that. Worst part of her is that she neither gives +EN after a fight, not reduces your EN consumption like the other girls, so you end up running out of EN if you fight a lot. She might look like a boss killer with her +TP and +DEF, but Tira with her crit buff was better.
Plugins:
Early on try to use the relevant location +damage addon, then take whatevevr else you can get, like armor penetration or ranged evation. Later on you get +crit chance and +crit damage. Combined with Tira and a good chip you get near 100% crit chance and +100% crit damage
automatons: They're quite powerful as they can distract your opponent from hitting you, and they're almost as tanky as you. Lategame you can really buff them with plugins and addons, but when you get the gold key, you already did the most difficult challenge.....Well, the knightcore did let me get through a few tough fights so it's okay.
TL;DR always get the latest armor+chip, keep your weapons up to date with upgrades and new weapons, and focus on either melee or ranged depending on the mission and what your strongest weapon is ATM.