One of the most relevant aspects to Yamato's character is her being aware of Luffy for over three years since her encounter with Ace. Yamato has known about Luffy longer than any of the other Straw Hat Pirates. Back when she met Ace, Yamato wanted to join him on his ship but was overwhelmed by fear to make the leap. Ever since that moment, she has been waiting for Luffy, confident that he will arrive in Wano Kuni. Yamato has shown belief in Luffy for three years without even having directly met him. And along with using "Oden" as a source of strength to keep her fears at bay, she has also relied on the eventual meeting with Luffy as a "hope" to continue forward. Contrary to how Kaido views Luffy, Yamato has fate that Luffy is able to defeat her father and assist in opening the borders of Wano Kuni. I don't think such a belief can be discounted so easily.
Not only has Yamato been waiting for Luffy but as illustrated in chapter 996 she has been conscientiously following their journey. Yamato is aware of the Straw Hat Pirate members, their nicknames and their bounties. Even their recent actions within Dressrosa, Yamato knows about it. Normally that may not be so impressive but this is Wano Kuni we are talking about, a closed border country where very little information about the outside world enters. Yamato did not freely come across such information. She likely had to put in serious effort to acquire any newspapers or information brought in from the outside world by the Beast Pirates. Such commitment from Yamato regarding the Straw Hat Pirates expresses her interest, esteem and admiration for and in them. The extent to which Yamato is "involved" only adds to Yamato's importance and potential chances in joining the Straw Hat Pirates because it reduces the amount of time needed for Yamato to familiarise herself with the Straw Hat Pirates, their adventures and their objectives. Yamato can hit the ground running as a Straw Hat Pirate if need be (important at this stage of the story).
Franky himself has become curious in Yamato and I believe such situations are indirectly crafting bonds and relationships between Yamato and the Straw Hat Pirates.
If it ends up being revealed that the Octopus who guided the Straw Hat Pirates to Wano Kuni was stationed there by Yamato because of her belief in the Straw Hat Pirates arrival, it would majorly help Yamato's chances of joining the crew as it would establish that Yamato had a role from the very start of the Wano Kuni Arc.
Yamato could not leave Onigashima due to the explosive bindings Kaido placed on her twenty years ago. Despite her desire to want to open up the borders of Wano Kuni, she could not leave Onigashima to head to the main Wano Kuni Island(s) to confront Orochi and defeat him. There was only one day each year where Orochi visited Onigashima (Fire Festival) and during that time both Orochi's forces and the Beasts Pirates were gathered. Too many for one person to handle. Overwhelmed by such a task (defeating both Kaido and Orochi), Yamato began to rely on her belief in Luffy. And in believing Luffy's arrival was inevitable, Yamato could have created the plan to combat her inability of leaving Onigashima by using an Octopus (a friend of Yamato's who had the freedom to traverse the oceans) to help the Straw Hat Pirates enter Wano Kuni when they arrive near the Waterfall entrance (she already knew they were heading in that direction after the events on Dressrosa). The Octopus seemed to be attracted aboard the ship after noticing the Straw Hat Skull Flag. And the Octopus only revealed itself and began to summon the Koi Fish after Luffy mentioned his name on the transponder snail (chapter 910).
Additionally, for someone who is so in awe at individuals who lead adventurous lives and in the stories detailing such, I honestly cannot see Yamato remaining on Wano Kuni after the arc. Whether it is through the Straw Hat Pirates, as a representative of Momonosuke (Wano Kuni) or as a mere adventurer, Yamato will journey outside the border of Wano Kuni and explore the world. The wonders that reinforced her conviction and expanded her dreams will ultimately have substance added to it.
Another curious development I did find interesting during the Akazaya Nine's battle against Kaido is that none of them learned the Oden Nitoryu (two-sword) Style directly from Oden (a sword style Oden had considered to be the greatest there is). The Akazaya Nine's imitations were imperfect and as Kaido stated, weak. With Oden dead and none of the Akazaya Nine learning the two-sword style directly from Oden, does this mean Oden's two-sword style is forgotten? I don't think so. Oda has illustrated
at passing on his sword style to his retainers in the flashback so even when Toki revealed to Oden why none of the Akazaya Nine wanted him to teach his sword style to them, I don't see Oden not leaving any trace of his sword style behind. In all likelihood, Oden wanting to leave the teachings of his sword style behind (for his son and future Samurai), recorded the techniques and training required within his Journal. The “very important things” Yamato mentioned when talking about the journal to Luffy could be the secrets behind Oden’s two-sword style.
Yamato may not have fully mastered the Oden two-sword style but I believe considering the admiration and reverence Yamato had for Oden, she would not have not attempted to learn the fighting style of Oden, especially if Oden had noted down the teachings within his journal. We have yet to see what Yamato can do with swords and when that moment arrives when Yamato wields swords, the Oden two-sword style will be reborn. And this is why the current meeting between Yamato and Momonosuke is integral. Momonosuke needs to know who Yamato is and develop sufficient confidence in her and her abilities to help inspire him to make the decision to give his Ame no Habakiri to Yamato. BOTH Enma and Ame no Habakiri will be used against Kaido.
And if Yamato does end up joining the Straw Hat Pirates, Ace would be indirectly responsible for such an outcome by inspiring Yamato with his stories of Luffy. As if a final gift from Ace, a new friend he was able to introduce to his little brother from three years ago. Just as Luffy has become closely connected to Tama because of her relation to Ace, the same is happening with Luffy and Yamato.
Narratively, there is just so much going for Yamato. Her potential is immense and my excitement for her is only growing the more Oda focuses on her. To know we have more on her past (mother), trauma, darkness, relations (Marco and Kaido), attack style (she will wield a sword/swords), transformation and dream (adventure, dawn, freedom) to look forward to, how marvelously exhilarating.
As for Yamato's design, I find it appealing and memorable. Personally, I would have preferred if Yamato had a more monstrous/non-human design (like Monet whose design I love). But with Oda teasing the readers to a potential transformation from Yamato, I really do wonder if Oda has a more beastly design for Yamato already planned. I also look forward to Big Mom's meeting with Yamato. They haven't met yet but when she meets Yamato, will Yamato's appearance and unique race (part Ancient Giant? Oni?) appeal to Big Mom's fascination such as with the non-human Straw Hat Pirate members (Brook, Jinbe, Chopper, Franky).
Aka Oni Yamato
(Red Oni Yamato) - a potential Epithet for Yamato that embodies both the Oden legacy and her own blood. 'Aka' inspired from the Akazaya Nine and Oni after the race she represents.