Karina: "Huh? Oh, um... well, it was just one tutor. His name was Marley, he was my general tutor for lots of stuff actually. Education, magic, history, other... stuffffff. He only started doing magic cause I kept asking him to teach me.
It actually took me a long time to learn how to, uh, control mana properly. Like, a couple years!"

Wow. That's almost four times as long as it took you. You could see it taking that long if you had to blunder it out on your own, but, she had a teacher. You had the Academy to speed things along.

Karina: "Anyway, I'm not sure about theories or methodologies really. We mostly practiced the fundamentals of controlling mana, and he helped me learn my basic healing spells. Most of my magic training was practical cause I asked him to teach me as a favor, instead of my parents hiring him for it. I haven't been taught much formal stuff."

Naturally! It's the first step to being a mage, of course. If you can't move mana, you can't move any power into spell sequences and cast magic.
The easiest way to learn, and how they did it at the Academy, is to have someone basically hold your hand with it and pass you mana or pull it out from you. That lets you get a grasp on the sensation of mana moving through your body. From there, it's just practicing replicating the feeling and building up your ability to control mana to the point that you can cast actually useful magic.
There's also the option of putting people into an environment with very turbulent mana. If the ambient mana is wild enough, even a normal person can feel it just from being there, but that kind of situation tend to be dangerous to exposed to for any extended period, ESPECIALLY for untrained mages.

Karina: "Mmm... Sorta similar! I had a lot of trouble... concentrating, for a while. So it was hard going. Actually, taking in mana wasn't too bad, I picked that up pretty quickly. But pushing mana out took moooonths! That was aaaawful, it was the only time I saw Marley get annoyed with me too. But I finally got the knack of it, and that's the most important part of casting spells! It took a while longer to get my mana control strong enough to actually trigger healing magic though, so it was a few MORE months of practicing and building strength before I could actually use magic and learn spells. But I did it!"
Ah, yes, you recognize some of these struggles. A lot of simpler magic can manage with small quantities of mana. A fireball with not enough mana will just be tiny and not very hot.
But with healing magic sequences, to prevent misfires, it won't activate unless the caster has sufficient mana and mana control. It also can't be amped up much compared to more 'direct' magic, like the fireball.
It takes a bit of practice to pick up the knack for adjusting mana input into spells, and you don't actually know any that are suitable for it right now.

Personal aptitude, mostly. Some souls retain mana well, some shed it easily, some have large capacities, others have small. Like a lot of things it varies by person, pretty normal. But for the most part it can be overcome with training and effort.
Sounds like Karina just naturally takes in and retains mana easily, which would make it somewhat harder to push it out.

Karina: "Ehehehe... Thanks! Everyone was surprised when I actually managed to use magic! I mean, I may have been a bit of a hyperactive child in the past BUT that doesn't mean I can't focus my energies!"
Frederic: "I for one was tremendously glad she found a creative outlet. Of course, it led to this Adventurer thing, so I have mixed feelings."
Karina: "Psh. He secretly likes being back to having fun and flexing his muscles. Would never admit it though."
Frederic: "My first and foremost concern is your safety Karina."
Karina: "See? Can't be true to his feelings, poor guy, tut tut. His second concern is totally punching monsters."

Frederic: "Yes, that's right. Most of the people I fought alongside were normal people with no magic or will, so they had to get along with a sword, a shield, and good training. My training was always abnormal, since I've been missing my left arm since birth. I can't use a shield along with my weapon, and most sword forms and standard training rely on at least having the other arm as a counterbalance. Most of my early 'career' was sparring and mock-fighting, hammering out what works and what doesn't for my body.
After I found out I was a will user, the few other will users in my lord's employ trained me in the very basics; feeling the mana in my body, Will physical enhancement, all that."

One interesting thing about Willpower is that, since sequence forming is so automatic to a will user, they can train to form sequences even with basic body movements. It's considered a pretty basic skill of Willpower usage, and it lets the user strengthen their body beyond normal human limits, allowing them to move faster, strike harder, and block more damage than a normal human could.

Frederic: "My actual Willpower hasn't ever diverged from the basic physical reinforcement, so I've just worked on sharpening that for years. As you saw with that Mana Burn thing I did, I've gotten somewhat creative with it. Which also meant that my training style has stayed the same, just sparring and exercising. Though, now I do incorporate some Will exercises into my routine, just using it to expend mana and improve my control."

The three of you spend the rest of the trip back to Madosa in comfortable silence, watching the sky pass by.



The three of you approach the Adventurer's Guild, carrying your slime prizes. You and Karina both have a small green slime in a sack, while Frederic carries a giant bag as big as he is, with the blue slime inside. This time, rather than entering through the front, you head around the side to an open area full of stalls. This is where larger and messier monsters and their parts are traded in, so as not to be bothersome to the people inside. There are dozens of people back here, all milling about and talking, most with some kind of beast or animal. One group has a very rotund silverish frog carcass that would come up to your waist if sitting. Another has several large animal furs, still with a bit of red tinge to them. One group of especially grizzled looking adventurers are grinning and laughing around a single horn as long as Frederic is tall. You see a few other new adventurer parties with slimes, same as you, though none have managed quite the large haul you have.
Madosa has relatively few dangerous creatures nearby, but its location directly in the middle of the four continents makes it a prime trading hub and adventurer's nexus, so despite the creatures around here being rather weak and easy to harvest, a great variety of things still come through the city.

You see an open stall with a woman standing behind it, and head over. You and Karina both lay your slime sacks on the counter, while Frederic sets his down with a large thud. The women greets you, then continues speaking as she peeks into the bags holding your slimes.
Woman: "Welcome! I see you've brought some slimes! Oh my, and quite a large one here too. Hm. Are you new Adventurers?"

Woman: "You are! We do take material turn-ins inside the guild for smaller items, but for anything larger, especially monster bodies or more... aromatic items, we have this outdoor open space.
Now, about your slimes."
She has you bring your haul over to one of several large scales placed around the square, each one easily big enough for all four of you to stand on, with a large basin already on the scale and zeroed out. The woman has you empty the slime sacks into the basin, and with your massive blue slime, it only just barely manages to all fit. She records the weight on a clipboard, then looks back to you happily.
Woman: "Did you manage to recover any cores from the slimes? We can accept those as well."
Karina: "Um, is it okay if they're damaged?"
Woman: "Well, they are somewhat more valuable if whole, but we can still accept damaged ones. There are various uses for whole ones, while broken are mostly relegated to being ground up and used as an alchemy ingredient."
Karina: "Ok! We have two whole and two cracked ones."

Karina fishes the four slime cores from her bag. Two small cracked from the battle on the island, one small whole from the slime that landed on the ship, each about the size of a large marble. The large slime's core is still intact, and much larger, easily 6 inches across. The woman gets a look of surprise when she sees the large core.

Woman: "Oh my! You mean that you recovered that large blue slime's core intact? I'm very surprised, that's quite a feat for a new adventurer group. Usually they would have to attack the core directly to subdue a slime that large. I will gladly take the small cores, but, do you perhaps want to keep the large one?"
Frederic: "What for?"
Woman: "Well, it is somewhat valuable on the market, but it may be more valuable to you as it is. A core like that could be made into some kind of equipment, or weapon perhaps. Nothing strong enough that a mid level Adventurer would consider it, but for a new party it could be a very useful investment. The total payment without that core would be 145 Drachmas, and I could give you 100 for the large core."