Rather than saying Robin has gone bad, it's more accurate to say Robin has awakened. In a certain sense, being sly is her true nature; she just spent a long time acting on her own, with only the little chameleon by her side.
Even though she has a sly nature, an Inteleon wouldn't feel much about it.
She spent quite a bit of time with Yamato during childhood, occasionally exposing this potential, but the rather single-minded Yamato never noticed this issue.
It was not until this moment that she realized Robin was just joking.
"Alright, I'll stop joking. Lord Arceus said earlier that once you return, you should go find him.
Also, were you serious when you said you wanted to go out with me? If it was just a joke, then I'll set out tomorrow."
"Oh, that, of course I want to go. Just wait for me a bit longer, let me see what the foster father needs. If it's something really urgent, then I'm sorry."
In a way, she had already postponed Robin once. According to Yamato's plan, she should have taken off after the banquet, but she encountered an irresistible force—a special summer camp from Arceus.
Robin was still here, partly because she was searching through materials, and partly because she was waiting for Yamato.
"No worries, if Lord Arceus has plans, there's nothing we can do about it.
By the way, the Corviknight's egg over there is about to hatch, you go ahead and take care of your things, I'll keep observing."
With that, Robin tidied up some documents; they were coincidentally a summary of the existing Pokemon on Ghost Island.
The more you observe Pokemon, the more mysterious they become. At this point on Little Sky Island, many scholars were enchanted by these mysterious creatures, to the point of living in a Tauros barn to study Tauros as enthusiastic scholars.
...
After stretching her body, Yamato jumped directly off the edge of Sky Island, considered a legacy from Kaidou's strange hobby.
Unlike Kaidou, she did not create a hole upon landing; just before hitting the ground, Yamato skillfully used her ability to steady herself, although she did stir up quite a wave on the Inner Sea.
Thud... Thud...
Because of Yamato, an unfortunate Pomfret was flapping around the shore, which was then picked up and thrown into the fish bucket by Page One.
"Yamato sis, did you really have to make such a scene right after coming back?"
Wiping the water from his face, Page One reeled in his fishing rod; the bait on the hook had long disappeared, that catch had failed once again, but no worries, since there was still fish in his bucket, although it wasn't caught by him.
By the way, there was currently only one fish in his bucket.
"Did I interrupt your night fishing?"
"No, I just cast the line..."
"Little Pei! Why are you here? I've been looking for you for five hours!"
"..."
Page One's lie was exposed, but fortunately, in front of him were Yamato and Ulti, no one discovered the fact he had been grounded for five hours.
"Yo, isn't this 'Kozuki Oden'? You're back too?"
"... Don't mention that! Forget that dark history! Don't force me to erase your memory physically!"
Compared to Robin's slyness, Ulti's directness is more unbearable to her. God knows how much effort she put into making sure Yamato wouldn't mention those four words. Now, being called by Ulti like this, she felt as if ants were crawling all over her.
"It's a bit difficult~ Alins, by the way, I made a small gift for you."
Saying that, Ulti pulled out a kimono-style Yamato doll, though not marked by text, the doll was filled with the words 'dark history.' Mainly, the doll's eyes were too shrewd, leaving Yamato speechless.
"Darn it, weren't you on 'Ghost Island?' Otherwise, I'd definitely catch you for a photo!"
"Hmph, even if you find me, I'm not afraid; I definitely wouldn't say I'm Kozuki Oden.
But don't mention that, if you were two days later returning, Little Pei and I would have gone out too."
The celebration banquet ended; pirates don't get holidays. The turmoil from Whitebeard's dying declaration had completely fermented, most seas becoming exceptionally chaotic; there weren't many executives left on Ghost Island, the siblings were soon going out to execute a mission.
"Is that so? Never mind, not saying it, foster father is calling me, I'll go first."
Yamato put away the doll, even though it was 'dark history,' she wasn't angry. This kind of joke was within her acceptable range. If you looked at it carefully, the doll was quite cute, representing this special experience from another perspective.
...
After fooling around for a bit, Yamato still came before Arceus, enjoying the wonderful times without Kaidou.
"Thank you, foster father, glad you managed to send the old man away, otherwise it would have been troublesome."
"Don't be happy too soon, he will come back eventually; it was just giving you some space temporarily, I won't care about what happens afterward."
Arceus could have brought Yamato back earlier, but deliberately delayed it for a few days, letting her have more substantial interaction with the other Yamato.
During this period, Kaidou gave up on Yamato due to boredom, rode off on the eight-headed dragon to find fun, with many newcomers at The Sea to mess with, plus it doubled as a chance to search for Plates and scout for any talented newbies.
"No worries, it's always good to meet him later, but foster father, why do you need me?"
"Have you gained any insights this time?"
"Um... That old man is indeed a jerk, if no one controls him, he'll become crazier.
And... governing a country is much more troublesome than I thought... and also..."
Yamato habitually critiqued Kaidou first, and then talked about her insights. Although nothing particularly insightful, there was some progress, enough to barely pass Arceus' evaluation.
"Foster father, is there anything else?"
"Nothing else, when you're out, be cautious, might face some dangers."
"Rest assured, foster father, I'll know to run if I can't beat them. Oh, by the way, this time I heard that Ace over there seems kind of silly, he was saved but was swayed by just one sentence to return...."
Yamato talked about her travel encounters without taking Arceus' words to heart. She didn't know that this sentence was an indirect hint from Arceus.
About Kaidou possibly blocking her halfway, the higher the score she achieved with Arceus, the greater the reward she would receive. If she harvested more from this "journey," Arceus would prepare to directly warn her to be cautious of Kaidou.
However, she only received a passing score, thus only getting some indirect hints.
Considering Yamato's situation, without triggering a special response against Kaidou, she did not grasp what Arceus was hinting at.