Note: This post has been updated for the possible Rahkshi discussion next week. It now reflects the Toa's personalities/backstories that were recently discussed. These new changes will be written in italics below the old info (mostly for Pohatu). This does not cover the personalities for the Rahkshi, just how they challenge the Toa.
So I was thinking about the Rahkshi discussion and noticed that a few of their "elements" should probably be changed. Namely Guurahk and Panrahk. I mean, if stone vs earth had such a debate, what about fragmentation and disintegration? Not only are they similar, but they don't really fit, in terms of how the other Rahkshi elements work. Panrahk/Guurahk's are physical damage only, while the others can all affect things from a mental/emotional level as well as the physical damage.
Turahk - Fear
Kurahk - Anger
Vorahk - Hunger
Lerahk - Poison/Venom (Poison is a bit tougher to see, but it serves to corrupt/taint pure things, and purity has more of a mental or spiritual connotation than just being physically clean.)
While searching for possible replacement elements, I also noticed some good character development if certain Toa fought certain Rahkshi. These fights would make more sense if they take place after Makuta is revived, since they wouldn't have been fighting the Toa seriously during the Mask of Time hunt.
These fights will be more of an internal struggle for the Toa. An external struggle can happen after a Rahkshi upgrade, and is discussed at the end of the pitch.
Tahu vs Kurahk - Tahu is a fierce warrior. He is brash and his emotions affect how he fights. So if he were to gain extra anger from Kurahk, it would affect him more. Anger at the state of the island, anger at the difficulty of their task, anger at struggling to be the leader of a team of Toa. He needs to learn to control his anger to better lead others.
Kopaka vs Turahk - Kopaka keeps his emotions bottled up, compared to Tahu, so he could do better against anger. However, fear would challenge him. He is a prince who swiftly became king. He has a duty to Ihu, and a duty to his Toa team, especially if he has the potential to take the leadership role from Tahu. It's a lot of responsibility for one person to handle. This responsibility would create fears in his mind. Fears that he won't be able to deal with it all on his own. And it's only made worse by him keeping the fears bottled up like everything else.
Gali vs Lerahk - Since Gali deals with water, it is obvious that purity plays a role for her. Purity of the water she uses, as well as purity of mind/spirit that makes her a good arbiter and a good mediator among the other Toa. Poison/Venom would pollute both of these aspects. The waters will become tainted, and so will her heart. The once calm, serene Toa will struggle to regain this purity so she can continue to help her friends.
Pohatu vs Vorahk - Until Pohatu's backstory is discussed, my current headcanon is that he was originally a nomad before finally settling down in one of the permanent villages to be a mahi herder (or possibly a lightstone miner now, going by the Candlehead discussion). But during his nomadic days, he would have struggled in the desert, with hunger and exhaustion being common occurrences to drain their bodies and their spirits. After settling down in the village, he would have put those memories behind him. But they resurface during his fight with Vorahk's draining powers. He must come to terms with his past to properly face his future.
In terms of my pitch, Star Athlete Pohatu pretty much kills the whole idea for him. However, I still believe these interactions are useful for development. To retain this specific pitch, I propose that Pohatu was originally a nomad who was good at his sport, but had no name for himself. He was just a plain old nomad playing on the sand dunes instead of a real field. Ahkmou spots his skill and recruits him to "make him a star". Pohatu agrees, because it beats hanging around a desert, trying to survive the harsh environment.
Lewa vs Guurahk - My headcanon for Lewa is that she's a cartographer. Her free-spirited demeanor gets the adventure and thrill of exploring the whole island with a Gukko's-eye view to map it out. This soaring feeling applies to her general personality too. So when facing Guurahk, she struggles against the powers of Gravity that will clip her wings and bring her high spirits crashing back down. She will have to learn to fight without relying on excessive acrobatics. This will develop her fighting skills, as she is likely still the "rookie" of the team. She will also learn that her free spirit can't be held back, even if her body is.
Lewa as the free-spirited orphan still works with this pitch. Bingzak can teach her some responsibility, but she still enjoys the care-free lifestyle.
Onua vs Panrahk - Onua is always seen as the wisest of the Toa, whose thoughts are one of his most useful qualities. Onua's strength comes, not only from his powerhouse of a body, but from the vast calmness of his mind. So when Panrahk appears with powers of Psionics, Onua will have a new challenge. Not many opponents can harm Onua from the outside, but psionics will use illusions and mind games to toy with the Toa of Earth. For someone who draws on wisdom, having something corrupt his thoughts will be devastating. The once wise Toa will wonder if his current state of mind is true wisdom, or a false mindset that could harm his friends instead of help them.
As a continuation to this pitch, the Toa overcome their internal struggles, and could then discover the true identity of the Rahkshi. The Rahaga of G1. As Matoran, they could have interacted with the Toa enough that it serves as an external struggle to counter the internal one they had. This struggle will swap the Rahkshi back to their respective region Toa.