Going back in time to save the Saintess of Light

"By my name, I will not allow you, O dark god which trample us all to awaken and wreck havoc across this world!" [saintess of Light]   "You, who easily toy around with life and death of my citizen, should perish once and for all!" [saintess of Dark]   The two of them, the saintess of Light and Dark, are now facing their destined arch nemesis, the Dark God.   The Dark God, he is an elder god alongside two other gods, that are believed to be born when the universe was filled with nothing but void.    This god, he does not have any particular form, the best description for his form is that he is formless and will take the shape of anything that he wanted to be. Be it from the elder dragon to a human, he will keep on morphing based on the situation he found himself into. A powerful and frustratingly irritating foe. The more time I spend fighting against him, the more I realize how he think of me, nothing more than a moth attracted to the flame   ~Smirk~ "Watch out for his attack! Level 9 thunder magic, thunder shield!" [Noble man]   A gruesome dark spear, the size of a Tyrannosaurus Rex was instantly cast by the dark god, targeting both the saintesses. It's strong, strong enough to make me cast a level 9 thunder spell just to fully block one of it, and even that wasn't enough to completely negate the damage as large crater with a radius of 3 meter form below the thunder shield of mine   ""Thank you"" [Saintesses]   For them, I would do my best. Both of them have sacrifices many things in their life. Time, effort, friend, money and even family just to fulfill their destiny as Saintess. The least I can do for my younger sister and her friend is to do the same.    "Miasma of Elder Dragon" [Dark God] "Level 9 thunder magic: Thunder dragon!" [Noble man]   As the two magic clash, my purplish thunder mana slowly become that of a black thunder, indicating that the dark miasma from that awful god started to win over my pitiful level 9 thunder magic. If only I could achieve level 10 thunder magic, then I could become more useful for the two of them   "Even so... I won't give up!" [Noble man]   All the mana inside of my body, gather it. Gather it and condensed every single bit of them into my heart, and let it strengthen itself so that   "Brother! Don't!" [Saintess of Light] "You will die!" [Saintess of Dark]   I will, but, so are the two of you. Each saintess, they all inevitably meet their demise once they seal the Dark God into the void.    "f*******n spell: Soul enhancement" [Noble man]   Right now, I'll use my very soul as a source of energy to fuel my spell. I don't know how long I can last. No, I don't even know whether I will become useful with this technique, but this is what I should do!   "Level 9 thunder magic: Thunder army" [Noble man]   Summoning a legion of army made out of my thunder mana, I made them rush head first into the Dark God. Their strength varies, as some are clearly stronger than the other. Some are infantry, while other took command as the commander   "Interesting. Miasma of Zombie King. Death incarnation" [Dark God]   The elder god response, simply mocking me by using some spell made for the undead. Again, the legion of undead he summoned consist of varying degree of strength and rank. Truly, an irritating foe this god is   The two armies clashes. With each hit of my thunder army, the death incarnation army of the Dark God is electrocuted, paralyze and unable to move, leaving it wide open for follow-up attack from another thunder army of mine.    Head splatter, brain squashed, bone broken, jaw dislocated, a gruesome sight, and yet what will happen shall the three of us, no, shall the two of them fail in sealing away the Dark God, it will become even gruesome.    "Light. Heaven Javelin" [Saintess of Light] "Dark. Hell candle" [Saintess of Dark]   The two combination attack wreak havoc on the battlefield. With the heavenly attack raining from above, like an archangel throwing their javelin onto earth, and the hellish black fire from below, with intensity that one would think it was cast by satan himself, the attack not only wiped out the army of death incarnation, but also make the Dark God scream in pain   """Ughh!!!""" [Saintesses, Noble man]   It's simply deafening. It literally burst my right eardrum as I can feel blood and the fluid from my inner ear leak out into my outer ear, dripping my shoulder a bit.    "Once more!" [Saintess of Dark] "Yes!" [Saintess of Light]   And the two of them repeat the same pattern of attack. You would think a being that is called a god would not fall for the same pattern of attack once again, and fair enough, he doesn't, as he navigates himself skillfully, but   "You!" [Dark God] "Level 9 thunder magic: Thunder pierce" [Noble man]   I can sense that the Dark God is getting restless, since I am also restless. Using my sword as a medium, I channel all my thunder magic into it, piercing through the Dark God. As he is currently imitating a faceless human, blackish blood drip out, and as I keep on slicing him, black colour intestines with it juices spurt out   "Not yet! Level 9 thunder magic: Electrocution" [Noble man]   This time, with my own bare hand, I grab his spinal cord from within and sent in wave after wave of thunder magic, electrocuting the god.    Like a crazy man getting seizure, his limbs shake violently as the thunder magic keep on electrocuting him.    "Electrocution! Electrocution! Electrocu..." [Noble man]   Changing form into Giant Elephant, he quickly stomps me before sending miasmal attack to pierce my heart. I can see one of my aortic branch leaving my chest before being burnt by him   This is bad. This is really bad.    ""Dark and Light:..." [Saintesses] "That spell!" [Dark God]   He is panicking, which could only mean one thing   "Level 9 thunder magic: Suicidal thunder explosion!" [Noble man] "Don't interfere!" [Dark god]   As he stomp me for the last time, I unleash all of my magic into him. I don't know what happens next, but strangely enough   "Please. Don't leave me behind!" [Young Saintess of Light]   This is...