Time slowly passed and Tom's method indeed worked, much to Natasha's dismay. His body started to get visibly stronger in just a week after he absorbed fifty years of his life force, breaking into a 'supernatural' level, and with that, one of the biggest limitations of the human race was subverted by him.
It was apparent he would never be a mountain of muscles since his body stayed lean and didn't get a lot of increase in volume but appearances could indeed be very deceiving in the supernatural world.
Natasha was not happy about it but when Tom lifted 300 kilograms barbell... with one hand as if it was nothing, she relented and called his physical training over. Of course, she still wanted him to spar with her occasionally and Tom could proudly say that he got his ass handed to him despite his newfound physical prowess.
His strength was only at the level of a low-rank devil so Natasha's skill still made her superior. Tom simply couldn't catch her. But on the rare occasion that he caught her even once, she was done for.
It was not only Tom's physical strength that improved. It was his endurance, stamina, agility, and overall the whole physical package. Anything that had to do with physique got boosted through life energy.
The only flaw of this technique was that it was not an instant boost like Touki. Tom needed a lot of time to evenly meld and weave his life energy into every part of his body and even a slight deviation could cause damage to him so he had to be extra careful.
But at the end of the day, it was much superior to Touki which was just a temporary stats boost rather than a permanent physique improvement.
Still, the Life Energy Absorption Technique surpassed Tom's expectations. He first thought it would take much more time to show results but fifty years of life energy dispersed all over his body in a week was not bad.
Unlike Natasha's fears, this technique did not decrease Tom's lifespan. Well, he wasn't exactly sure about this point when he started training it but much to his relief, it worked like Touki in this case. The life energy was still bound to him, just not in a separate energy pool. It was directly in his body finally being useful for once.
The Life Energy Pool was a bit special. Touki did use Life Energy to work but one either needed intense physical training or Senjutsu to be able to slightly put said energy to use. It was a very stubborn and lazy form of energy that did not want to be used. One literally needed to force it.
That's why Tom was darn happy for his Sacred Gear. It simplified things a lot for him but that was also why he wouldn't be able to do the same for Natasha. One's life energy could only be stirred by oneself.
Touki also did not decrease the Life Energy of the user. It was not like Mana or Demonic Power where one had a reservoir and could use spells until it was empty. Unfortunately, just like magic, Touki required focus to maintain. That's why one could almost never really see a magician use it.
It's not like there was a shortage of magic users who trained their bodies to the limit or that magic users didn't drool at the advantages Touki could provide. It's simply that using Touki and spells at the same time was deemed impossible due to the inability to split focus.
And no, not even the mind-enhancing spells that could let one use more strands of thoughts could help with that.
Tom knew he struck a gold mine with his Life Energy Absorption. No virtual downsides, no requirement for focus, no strenuous training, and permanent effect? Sign him right up!
By the end of the third week, Tom's body reached the peak physique of a low-rank devil after he absorbed a hundred and fifty years' worth of life energy into his body. It was obvious this was only going to get harder from there and would require more life energy to proceed but Tom wasn't worried.
Sarael finally started to make deals with the families with devils afflicted by the Sleeping Sickness and soon enough, Tom would get a source of life energy.
But not all was rosy during these last few weeks.
At Natasha's request, Tom worked with her to access her own Life Energy Pool and the girl was successful after a week of trial and error. The kind of brutal intense training she threw herself in... Tom didn't want to remember that. He had no doubt he would have developed mental problems if he didn't decide to selectively forget about it.
So... Natasha learned the basics of Touki through sheer willpower and determination.
Great, right?
Well, hell no!
The first thing the crazy redhead did was to try to imbue her friggin' Life Energy with the Concept of Destruction.
'Cuz it works for Mana so why not?' Was her dumb reasoning when she woke up after being in a coma for a week, her body on the brink of destroying itself from the inside out.
Who the heck does that!?
Honestly, despite his new stronger physique, Tom almost fainted from all the stress and exhaustion his red-haired adorable psycho put him under with her new idea.
With his body getting stronger, Natasha thought she was once again being left behind so she decided to push herself. Tom knew he was a bad influence on her with all the stunts he pulled but this was a bit too much even for him! At least he thought things through before attempting them.
The worst thing was that he could not do anything about it. Whatever method he tried to help her unconscious ass didn't work. Even his Sacred Gear was totally useless, the Concept of Destruction completely blocking it off. It was so bad that Tom's mind even led him to contemplate the possibility of asking Sirzechs for help.
He... really loved Natasha a lot more than he initially thought.
But that notion was firmly denied due to the consequences not only Tom would have to face but also Natasha if this secret ever came out before she was strong enough to defend herself. At best, she would have been instantly killed and at worst, she would have been made into a breeding mare for half-devils with the Power of Destruction.
No way Tom would try to go that route.
Thankfully, as the most stressful week in Tom's life was half over with him only going half-insane, Natasha's state actually showed a sign of improvement so Tom could sigh in relief.
And she did get better. Even benefited from it too as her physical body got refined by the Concept of Destruction. It was not on the level of Tom's Life Absorption Technique. Unlike what Natasha desired, the main effect of what happened to her was not to strengthen her body. That was simply a happy side-effect. If Tom had to describe it, he would say her body entered a preparation stage to reach its 'True Form'.
Oh, Natasha reaching that stage was still a long, long way ahead of her but her body now had a chance to... evolve, for the lack of a better term.
There was a reason why nobody from the Bael clan ever reached their 'True Form'. Even Sirzechs attained it through the boosted control of his demonic energy provided by the Gremory Bloodline. The poor sod didn't even try to conceal that in his training memories since he didn't expect the one receiving them would have the Power of Destruction.
Sirzechs control over his True Form was nevertheless shaky as heck. In it, he was an all-destroying machine that would not differentiate between allies and foes. It was just... bad. And that was with boosted control.
No wonder the man sought peaceful solutions and avoided showing off his power, coming off as a useless beta male most of the time. Tom would have been afraid to release his power to intimidate others too if the side-effect of his control slipping even for a millisecond could have been the total destruction of an entire city.
But back to Natasha's foolishness...
Tom never told her but the Concept of Destruction was refining her body since she gained the connection to it anyway. It was just a very slow-going process and in a century, she might have gotten strong enough to reach high-rank physical prowess if she did no training on her own.
It was within the norm of passive power growth for noble devil offsprings so Tom didn't find it anything impressive. Natasha's little stunt, however, sped up the process immensely. She was not gonna get rank-ups in a matter of weeks like Tom but unlike the previous benchmark of a hundred years, Tom estimated her to be able to reach high-rank physical prowess in a decade.
Ten times faster improvement was a lot. And if she actually trained and actively used her Power of Destruction, Tom could not give a proper estimation of how fast she could have gotten stronger physically.
Then again, considering she should have been dead, Tom would be upset if she didn't get at least this amount of gains for her stunt. He had no idea how but she pulled through it with sheer willpower, keeping the Concept of Destruction at bay until her Life Energy got adjusted to it.
Unlike Tom, Natasha could not strengthen her body with her Life Energy as it was still firmly resisting leaving its energy reservoir. Now more than ever and Natasha actually lost her ability to use Touki in its entirety.
Serves her right for being thoughtlessly reckless.
Though, Tom did spank her silly for that stunt and made her promise to not be so foolhardy again but having some tangible consequence like the loss of Touki was a good thing in his opinion. It would make her think twice before doing stupid stuff like that without consulting him first.
Even if doing that got him called a hypocrite by her.
He would happily be a hypocrite if that kept her from more ideas like this! And he thought he was supposed to be the suicidal one between them.