The soul's ability to retain the energy used in the transmigration or reincarnation into another world, and actualize it by using the strong desires of the individiual is put into question here.... more>>

At the moment of death, if you wished from the deepest recesses of your soul for pain to stop, then your new body will be resistant to pain. If you wished for the coldness of energy leaving your body to cease, so shall it be that your new body would be resistant to cold. What if you prayed that in your next life you'd be devilishly handsome? Perhaps you'd gain a skill to charm the masses? What if you believed that in your old age, your final moments as you left this world were filled with wisdom and dignity? Something or someone may answer that wisdom and advice you, like a sixth sense.

Tensei slime acknowledges the idea that souls, in a magically oriented world, are a feasible source of energy. Souls are energy that are malleable in their raw state, but require a focus such as a steady supply of mana or a specialized status system or a corporeal body to guide its growth.

The intent of the soul is to answer the wishes of the individual or individuals who comprise it, their power is self referentially vast but fragile without a carrier to contain it, and their focus is reliant on several possible ways to become permanently tangible. <<less

The world of civilization is in its infancy, and therefore the system of magic itself is in its infancy. The magus of genesis actualizes the principles of focus and intent and places it in the forefront of the plot. ... more>>

If an incantation focuses magic to manifest, then if you make the incantation longer, then the spell will be more powerful right? If you believe hard enough then, you can command the winds to help you fly! This system of magic is literally being written by imagination in real time, and limited only by its compatibility with the natural laws of nature! <<less

Hmm... How best to explain this?... more>>

...

A human has a variety of skills. These skills vary in proficiency depending on how much someone has exercised this skill. So the deeper your comprehension of the basics of this skill, the greater the translation into real world application.

Magic just so happens to have created a system where all your "skills" are actual abilities with numerical aptitude. 

Can you do arithmetic? Boom! you have a higher thought processing skill. Do you know how to sweep the floor? Boom! You get a land clearing ability. And so on and so forth. You can also learn skills from people who have them and teach to those who don't.

The MC seems to be a supergenius of some sort, as he almost instantly masters any skill he learns, which he further synthesizes using his modern knowledge, consolidating them into stronger world breaking skills. ...there's a secret there. <<less

I have to admit, despite my love of the world building and story in this novel, the magic system gives me a huge headache.... more>>

The magic here feels very freeform, with magic proficiency and skills receiving names automatically with reasoning seeming to come from the fact that they are simply acknowledged as such. 

At first it seems that the experiences of a person prior to going over to a new world translate directly into usable skills, but it quickly devolves upon the introduction of racial traits and divine intervention.

Upon being born in this world one receives a status, which gives numerical values to your physical and magical attributes. Then you are given either a job or rank status, who determine the ease of learning and mastering certain skills. Finally you learn these skills, organized but not entirely exclusive to three main groups. 

Craft related skills(not really called this), which feature skills such as beekeeping to tailoring to smithing to accounting. All skills which generally have something to do with doing everyday work.

Combat skills, which dictate the names of special moves that an individual can use in battle as well as their proficiency in certain fields of combat. These can be as simple sword sproficiency or spear throwing, to as wacky and far out as biting skill or limb throwing.

And finally magic skills, each individual has an aptitude for a specific attribute and its branch of magic. You have the normal four attributes of water, earth, wind, and fire all with their own specialized skills. But then you throw in attributes like life, death, time, and void and things get a little bit complicated. 

Anyone with a certain level of understanding and aptitude towards crafting, combat, or natural sciences can learn certain skills that are made easier or harder depending on your race, job, rank, divine protections, guidance, consolidated skill proficiency, etc...

It's a mess. BUT I still absolutely love the story. <<less

A classic story to be sure, and a magic system based on real world myths and legends.... more>>

Index Librorum Prohibitorum, has collected tens of thousands of magical grimoires containing knowledge of Voodoo, western sorcery, Chinese deities, Aztec mysticism, Shinto legacy, seraphic hiearchy, alchemy, and many more. All of this forbidden knowledge is used to interfere with the natural laws of the world. Indeed... Within the universe of Index, magic was made manifest on earth in jealousy of the natural esper abilities of super science, a number of groups all tapping into other strange worlds and consolidating their energy into rituals, spells, and symbols to grant them power over the material world.

There's a strange mix of science fantasy that has one questioning if magic and science were ever really sperate in this universe... <<less

The main character, who seems to suffer split personalities due to reincarnating, comes across a startling discovery when he covers either of his heterechromic eyes.... more>> He can see the manifestation of elemental magic power depending on which eye he focuses on. His heterechromia thus offers him the unique ability to wield two different elemental magics, and even combine them. <<less

Scholars invented incantations to focus magic and make it usable by the majority. In line with the belief that incantations should strictly follow the guidelines set by the ancient pioneers of magic, invocation should be memorized word for word with no deviation.... more>>

Right...?

But what if changing a single word makes the spell more powerful? Or using an incantation with similar wording changes the nature of the spell entirely? How about if just shouting one word with a strong image in mind produces a weaker but more convenient effect?

This story questions the very basics of what little is known about magic in this world, in pursuit of the best application of magic according to different situations. The enemy won't always wait for you to finish chanting, or even stay still in one spot like a dummy, for that matter. Versatility and flexibility in the focus of magic is key to perfect control of magic here. <<less