According to Donan, the shadowy figure gave him the knowledge of how to learn only Dragon's Heath. However, according to Leon's experience, it was clear that there was a version of that skill that increased his mana and stamina passively. Although at the level max, those skills would only increase his health, mana, and stamina by ten thousand points, it was more than enough for him to find a way to learn the others.
Regardless, the other skills would be useful, but Leon wouldn't focus on them for the time being. Once Donan ended the lessons, his eyes were more dead than before. He was just looking at Leon, waiting for him to cancel the spell.
"... May I ask you a favor?" Donan asked.
"I will do everything in my power to protect her," Leon replied.
"I don't think you have any use for it, but you will always have my gratitude," Donan bowed.
Leon canceled the spell, and Donan disappeared. Although he didn't owe any favors despite everything, Leon indeed would do his best to protect Darya. He couldn't tell what happened to her until now, but she was a friend, and she was as important to him as the people he cared about on Earth.
"Well, moving on..." Leon said and then turned around to change his mood. "It is time for the next experiment."
To create a replica as powerful as himself, Leon had to spend twenty-five thousand mana points per second. Still, once he noticed that to keep Donan existing, he used less mana. Leon noticed that he could create a copy of himself with a lot less mana. The copy would have to be weaker, but that also meant that Leon could summon monsters from his memories and absorb their minds. Perhaps that would increase his growth speed. But for the time being, Leon decided to summon a copy from the moment he woke up on the island.
"AAAAAAAAAAAAAARRRRRRRRRRRRRRRGGGGGGGGGGGHHHHHHHHHH!" Leon's copy screamed in pain while lying on the ground.
"Ah... I forgot to summon a version that wasn't about to die," Leon frowned.
In the blink of an eye, Leon healed his replica, and the replica looked at him astonished when he saw himself... things were about to get very confusing, so Leon decided to use Sleep and pass some of his memories to his replica. When he wakes up, he would probably understand everything and help Leon.
"Mmm... five hundred mana points are being consumed per second," Leon said while he was analyzing his replica body. "It is weird, but I guess instead of the power, the older the creature is, the more mana will be consumed."
Perhaps the amount of knowledge the summoned creature had also influenced in that. It was hard to be sure... Regardless, when the replica woke up, it understood the situation. Although it was weak since the two Leon's had a massive gap in experience, both of them could feel a link connecting them. After processing everything for a while, the replica looked at Leon.
"So... you want to use me to get stronger... is that it?" The replica asked.
"No, I want your cooperation to get stronger," Leon replied.
"What will happen to me once your training ends?" The replica asked.
"You will return to my memory," Leon replied. "Don't worry, even though you will obtain different experiences, your existence will be safe in my mind. If you are unsure about that, then we can test it."
The replica nodded, and Leon canceled the spell. After a while, he summoned that same replica, and as expected, he didn't remember anything happening. The replica only existed when Leon used his mana to keep its existence.
"Well, time to do some more tests," Leon said. "Although it would be useful if you could use several skills and while I can give you the knowledge necessary to do so, it won't be necessary. For the time being, all you need to do is to meditate."
The replica nodded and just sat down and started to meditate. Leon could feel some energy gathering around the replica. Still, it would take time before that energy becomes an increase in mana or intelligence. Regardless, even though it was a bit dangerous to summon the same replica over and over again, Leon decided to force his control over it. Being a replica or not, it was a copy of himself from the past. Although it was fine to use Mind Control or keep erasing the memories of the replica in order to keep it obedient, Leon didn't want to mess with his past self. That kind of action won't change anything in the real world even if Leon creates some replica to increase his mana and intelligence, but Leon still wanted to be cautious of his own actions in order not to let himself fall on a dangerous road.
After a few hours, Leon felt that meditation finally increased the replica's mana and intelligence, so Leon decided to assimilate that knowledge by copying the memories of the replica. Still, when he did so, nothing happened.
"He got a bit stronger, but the consumption of mana didn't increase... and I didn't obtain one extra point of mana and intelligence either. I guess since usually, I have to meditate for almost a day, the same amount of experience acquired is necessary for my mana and intelligence to increase... even though a replica probably would have increased its intelligence and mana several times."
Leon also tested that theory... after letting his replica meditating for a full day, Leon assimilated the experience.
Congratulations! Your Mana has increased by one point.
Congratulations! Your Intelligence has increased by one point.
"Assimilation completed... assimilation... assimilation..." Leon frowned. "This world really sounds ominous.