Was asked to grade this, so here it is:
Turn 1:
Nice start from Kooljay, choosing a wide area attack and then a focused one. Nothing flashy, despite the element, but to the point nonetheless. Mirai's counter is solid, absorbing the first attack and then using it to destroy the second. Though I would have liked more description on how exactly you (Mirai) used the Yang hair gauntlet to destroy the 3 Storm birds simultaneously, as Kooljay had described them like pincers closing in at your sides while the third went straight. The fireball after that was simply to gain tempo. I give this turn to Kooljay.
Turn 2:
Tempo which Kooljay fails to regain, instead choosing to 'seal' the fireball, ignoring the shockwave from Mirai's Taijutsu technique, set up a terrain effect, and then attack. As to whether or not Snake Feasting is a Fuinjutsu or otherwise chakra-based technique, the answer is that its a basic summoning jutsu only able to remove (not seal) techniques of base rank and damage (up to 80). Mirai's fireball was well over what the snakes were designed to devour and as such they would have not been able to. Mirai takes advantage of this disjointed response (even without the Snake Feasting failing) by attacking with a shockwave as soon as the snakes left, permitting the storm clouds if only to make Kooljay waste chakra, followed by a very apt Genjutsu to disrupt his Byakugan. I give this turn to Mirai.
Turn 3:
Kooljay finally regains his momentum by plowing through Mirai's shockwave with an empowered jutsu. The latter reacts with a speedy dodge and simultaneous maneuver to pressure Kooljay whilst defending from the Rain dragon, again only permitting it to waste chakra as the second dragon's straight dive would have missed anyway following the dodge from the first one. Would have liked to see a more direct/offensive use of Chakra Shroud after the dodge. I give this turn to Mirai all the same as their move was more tactical than Kooljay's double-dragon approach.
Turn 4:
The use of Zeus' Robes to absorb Mirai's chakra arm attack and nullify it while replenishing your reserves was nice. The Water + Lightning combo afterward was also a great addition, but note that Wave of Inspiration only has a damage value when used in its unfocused form. When used to augment a Water technique like Kooljay did it simply adds +20 to that technique instead. This means Sparky's boost is wasted as Wave of Inspiration has no damage of its own in this scenario.
Mirai's response is iffy here. With a base speed of 12 (6 AGL), Storm had surged forward using Perfect Sage Mode speed, which is 48 (12×4). Mirabelle attempts to dodge at 20 speed (base speed of 10×2 from turning into Dark Vacuity) and avoid the Water + Lightning combo, which in my opinion would fail, as Storm would have closed the distance between you near instantly while attacking with a technique that has a very wide AoE which as noted in Rift Walker's description, is quite troublesome to dodge, especially on such short notice. I give this turn to Kooljay.
Now after tallying up these results it would appear as a tie, but Kooljay's turn 2 misplay of trying to use Snake Feasting as a pseudo-Fuin jutsu cost him this fight. Reason being it was the most damage sustained in the entire fight. Even Mirai's turn 4 slipup would have caused them to only take 65 DMG (145 - 60 (+20 [elemental strength to Lightning and Water]). Kooljay ate 140 DMG to the soul. Winner: Mirai