Deep underground, Fey and party battled greater iron leaches (1), metallic gecko-like lizards that were almost as high as Sirena's shoulder at the head and much longer than she was tall. The monsters tended to act in short bursts of activity with subsequent fatigue, making them susceptible to group attacks, but had moderately high physical and magical defence.
Aiming for blunt force damage because her punching blades were too short to pierce vital points on the giant lizards, Fey hammered a Back Kick into her opponent, leaving a deep dent in its skull - but also sending her flying several paces in the opposite direction. Making an inarticulate sound of frustration (something like "nuugh!"), she turned herself around and ran back to the leach to finish it off.
Fey was running into a similar problem to Amethyst with her Whip attack, an imbalance between the strength of her attacks and the mass needed to keep herself from flying away due to conservation of momentum. She already had an element of this affecting her sparring ability in real life, but this was exacerbated manyfold by her increased strength in-game and the permanent halving of her weight upon the transformation to avariel.
Leandriel's role in the party was currently to act as a shield/guard for Sirena and Mimi to freely attack, mainly because his passive intimidation against level 60 monsters was such that they did everything possible to stay at least a hundred metres away from him and he therefore could not join in melee battle without chasing the leaches away from Blade and Fey. As such, he mostly stood around (looking intimidating) while using aura buffs to help the party and launching the occasional divine magic ranged attack that kept his kill count on par with Fey's. None of this required much concentration, so he spent most of the time watching Fey. (This is one of those occasions that is either cute or creepy depending on the relationship between characters.)
After an hour of observation, Leandriel concluded that Fey did not have some underlying purpose behind her frustration-inducing fighting style, no skill or ability she was trying to unlock. Not wanting to embarrass her, he sent a suggestion via private audio channel. "Have you considered using Inertia Increase?"
Fey's head immediately swiveled in the angel's direction, destroying any chance that their communication would not be noticed, but she replied in the same channel. "What's that?"
"One of the settings under the avariel transformation menu."
Fey's expression made rapid shifts between the distant look associated with accessing a virtual screen, blank non-understanding, puzzlement, excitement, and finally the somewhat unsettling focus associated with intent for rigorous experimentation.
Eyes locking on a nearby lizard, Fey charged, launching herself into a picture-perfect spinning jump roundhouse kick a few paces away.
The whole party paused at the deafening gong-like sound that resulted as the leach collapsed, neck broken, a deep indent in its head that precisely matched the shape of Fey's foot and shin armour. Fey herself landed neatly beside the felled beast, no backwards recoil to speak of.
Eyes alight with manic delight, Fey went on a killing spree. Her moves looked straight out of a cartoon, flashy kicks with jumping and spinning that landed with the impact of a sledgehammer despite the slender build of the attacker.
Blade watched Fey's newfound destructive capabilities while fighting his own leach, wondering what strange new ability she had unlocked. He was never truly surprised at anything his party did anymore, each of them being so exceptional in their idiosyncratic ways that his sense of normal had been recalibrated.
The most disturbing part about the whole thing, Blade decided, was Leandriel, who was easily tracking Fey's accelerated path of death with a soft expression on his face, like she was being cute. He shook his head and kept his mouth shut; clearly the angel was a goner.
Leandriel chuckled to himself. The Inertia Increase (2) ability built into the avariel wing magic was designed to help negate the melee combat disadvantage associated with having mass halved upon transformation, even when the wings were not summoned. It worked by reserving part of the player's maximum mana, rendering that portion unusable until the magic was released. In exchange, the player's effective mass was changed proportionally to the amount of mana reserved. For the average warrior build, approximately one tenth of their mana would be reserved to restore them to their pre-transformation mass. Based on his observations, Leandriel judged that Fey was currently throwing her entire mana stores – somewhat larger than the average warrior's due to her rogue class and innate talents at figuring out Fantasia's spellcasting system – into the ability, turning her from a half-Fey (the unit) Fey (the person) into a ten-Fey Fey.
When all the monsters in the immediate vicinity were dead, Fey turned and ran straight for Leandriel. He unobtrusively repositioned his feet for better balance, prepared to be hit by half a ton of elf.
He almost unbalanced in the other direction when Fey threw her arms around his neck with hardly an impact, having thrown her magic reserves into decreasing her effective mass instead.
"You're great," she murmured, leaning her head against his shoulder.
Leandriel half-sighed, half-chuckled, wrapping his arms around Fey's waist. He did not think he would ever get used to the unreserved emotional warmth she radiated, nor did he want to.
He was a bit slow to let go after Fey let herself slide to the ground.
She pulled a bottle out of her belt pouch and handed it to him. Leandriel looked at the stamina potion quizzically. "What is this for?"
Fey gave him a mischievous look. "I want to do something really stupid, and I'm going to need that afterwards."
Leandriel frowned in concern. "What is it?"
She gave him another cute look instead of answering. Leading the way to the next cavern over, this one full of fresh leaches, she said, "Thirty seconds."
In a flash, she was gone, and the chaos began.
Fey activated Self-Haste, then threw the rest of her mana into Inertia Increase. With her mass increased to ten times its original and her speed doubled, her strikes could now send the heavy lizards flying through the air.
For the thirty seconds her speed ability lasted, she was invincible, killing leaches so quickly that most of them did not realize they were under attack before collapsing to the ground, heads and necks crushed.
She destroyed the last of the monsters in the cavern with a few seconds to spare, walking calmly back to where she had left Leandriel. Then she swayed and collapsed.
Muttering a swear word, Leandriel caught her before she could hit the ground. Discarding the stamina potion Fey had handed him, he pulled a much stronger one out of his pouch and poured it into her mouth, followed by a greater healing potion. The amount of damage she had done to herself by moving that much extra mass at double speed would have killed her if he had not intervened in time.
Fey's complexion, gone almost grey with exhaustion, gradually regained the pink of health. She stirred and opened her eyes.
"Do not ever do that again," Leandriel commanded.
"Okay," Fey said agreeably, still lying bonelessly in his arms.
Leandriel opened his mouth to argue, then closed it, stymied by her quick capitulation.
"You can yell at me if you want," she assured him. "But I was pretty badass back there." Another impish smile.
Something – he did not know if it was his control or his temper or something else – snapped. Instinctively raising his wings as a visual shield, he kissed her.
When he raised his head, it was to see Fey's eyes almost circular in how wide they were. In his current mood, he held her gaze, unapologetic.
"You two done playing over there?" Sirena called from the first cavern, where leaches were starting to respawn.
As if to show it was not a mistake, Leandriel kissed Fey a second time before helping her to her feet and strolling back to his position guarding Sirena and Mimi.
Fingers hovering over her lips, it took Fey a few seconds to ascertain that she could walk. Steps unsteady, she made her way back to the main party.
Her thoughts flashed to the devastatingly devilish smile Leandriel had shot her before letting her go, and she stumbled.
Meekly taking her place in the party's fighting formation, Fey reflected on how she was a bad influence.
(1) The name of this monster is based on the word 'leach' and the largest gecko in the world, Rhacodactylus leachianus, commonly known as the Leach's gecko (or 'leachies') or New Caledonian giant gecko, named in honor of zoologist William Leach
(2) The initial design of this ability was to increase inertial mass without increasing gravitational mass, but it was decided that that would be too confusing both to write and for a player to figure out how to move without falling over. The name remained Inertia Increase because alliteration is pleasant. Inertia is the tendency for matter to stay at a constant velocity when not under the influence of an accelerating force. Gravitation refers to the tendency for mass to accelerate towards other mass. In the phenomena measured to this point, all matter has the same gravitational and inertial mass (i.e. if their mass as measured based on their gravitational properties is 1kg, their mass as calculated by their inertial properties is also 1kg.)