Every companion and enemy in the game has a variety of stats that can be modified for different benefits.
HP - Every character has a maximum amount of hit points, or HP, they can have at any given time. Every time a character takes a hit, they lose hit points. Once they reach zero, the character is defeated and cannot make anymore moves except for abilities that activate upon death or until they are revived. Characters can be revived in and out of combat at any time through the use of items, spells, etc... except in special cases like when a character is defeated through predation. If a character is not defeated, HP can be restored in a variety of ways such as items, skills, or abilities. The maximum amount of hit points that can be attained can be raised temporarily through accessories, skills or abilities or permanently by leveling up or by using seeds. Additionally, HP is sometimes used to activate Physical or Magical skills. Since it it easier to restore, HP cost skills generally have more uses than MP or SP skills but they take away percentages of health, instead of a set amount and they bring your character closer to death making them risky in some situations.
MP - Every character has a maximum amount of mana points, or MP, they can have at any given time. Mana is primarily used for casting spells but some some physical skills use MP too. Generally, mana is hard or expensive to restore but you get a lot of it so it's useful for casting many powerful spells in a short period of time. For longer fights or deep dungeon crawls, mana should be conserved unless you can easily replenish it. The maximum amount of mana points that can be attained can be raised temporarily through accessories, skills or abilities or permanently by leveling up or by using seeds.
SP - Every character has a maximum amount of skill points, or SP. At the beginning of every battle, a character starts with half of their maximum SP points but that can be increased to three quarters or full SP with abilities and equipment. SP is used for most physical skills but certain types of magic use SP too. SP is gained by attacking or defending, but defending nets you double the amount an attack would. The maximum amount of skill points that can be attained can be raised temporarily through accessories, skills or abilities or permanently by leveling up.
Attack - Modifies physical damage dealt by most weapons such as swords, clubs, hammers, etc...
Defense - Modifies physical damage received.
Magic - Modifies magical damage dealt by most offensive spells such as Black Magic.
Willpower - Modifies magic damage received and the power of most White Magic and Holy Skills, whether damaging or healing.
Agility - Modifies turn order. The character with the highest agility goes first in a round of combat followed by the second highest, then the third and so on. Some moves are faster than others and can increase a character's priority in turn order without increasing agility. It also affects the physical the damage of some weapons such as Rapiers and Spears.
Dexterity - Modifies the damage of pleasure attacks and some weapons such as bows and boomerangs.
Hit Rate - Determines the chance of hitting your target. At 100% you will always hit your target unless their evasion rate is above 0%. Hit Rate can be raised beyond 100% to increase the chances of hitting evasive characters.
Critical Rate - Determines the chance of getting a critical on a hit, dealing double damage. For example, if your critical rate is 50%, whenever you score a hit, there is a one in two chance that it deal double damage. Raising it above 100% does nothing.
Evasion Rate - Determines the chance of dodging a physical attack. Some attacks cannot be evaded.
Magic Evasion Rate - Determines the chance of dodging a magical attack. Some attacks cannot be evaded.
Counter Rate - Whenever an enemy makes a physical attack against a character, hit or miss, there is a chance to do a counter, dealing physical damage to the attacker. Counters cannot be countered or reflected.
Magic Counter Rate - Whenever an enemy makes a magical attack against a character, hit or miss, there is a chance to do a magic counter, dealing magic damage to the attacker. Counters cannot be countered or reflected.
HP Recovery Rate - After making their move in a turn, a character will restore a percentage of their total HP.
MP Recovery Rate - After making their move in a turn, a character will restore a percentage of their total MP.
SP Recovery Rate - After making their move in a turn, a character will restore a percentage of their total SP.
SP Charge Rate - SP recharges at a default value of 1 SP per attack and 2 per defense. This can be doubled with abilities and equipment in Part 1.
MP Consumption - Modifies the base amount of MP used by an ability.
SP Consumption - Modifies the base amount of SP used by an ability.
Recovery Effectiveness - Modifies the potency of recovery effects on this character such as items or skills.
Item Effectiveness - Modifies the potency of items used by this character.
Steal Success Rate - Modifies the chance of success whenever a Thievery and some Special Skills are used.
Magic Reflect - The chance that a character will reflect a spell, taking no damage and dealing it to the enemy instead. Reflected spells cannot be reflected.
Exp Rate - Modifies the amount of Exp earned at the end of every battle.
Job Exp Rate - Modifies the amount of Job Exp earned at the end of every battle.
Gold Bonus - Modifies the amount of Gold earned at the end of every battle. This does not stack across characters. The character with the highest Gold Bonus determines how much is received.
Item Drop Rate - Modifies the chance of an item dropping from a enemy at the end of every battle. A single enemy won't drop more than one item at a time. This does not stack across characters. The character with the highest Item Drop Rate determines the chance of an item dropping.
Recruitment Rate - Determines the chance an enemy asking to join your party. This does not stack across characters. The character with the highest Recruitment Rate determines the chance of joining.
Affinity - Value only for enemies showing how much they like you. Default is 25 out of a potential 100. Primarily it increases the chance of an enemy asking to join your party. (Note: This value is distinct from recruitment rate. See Companions for how the recruitment formula is handled). Additionally, at higher values enemies will give you items such as gold, food and weapons. Affinity can be raised by talking to enemies and by giving gifts that they ask for. Refusing to give them anything won't lower their affinity but responding to questions with obviously wrong or joking answers may lower affinity. Some advanced talk skills can make requests of opponents at the cost of affinity. Bosses and enemies that cannot be recruited through normal means still possess Affinity and the benefits that follow. There are a couple of monsters that refuse to interact with Luka under any means and whose Affinity is not meant to be raised, but can actually be increased through skills like Praise, although this yields no benefits.
Affection - Value showing how much Companions like you. A companion's affection can be increased by having him or her participate in a battle, (+1 per victory) and by giving various gifts. At higher values, Companions will give Luka gifts and will take "Requests" from Luka. Affection cannot be lost except through some gag gifts such Rocks and Weeds.