It was about two week after Shakara turned into her first stage, and she just seemed to be really stressed.
"Shakara, are you okay?" Avaritia asked her daughter, "Yeah, it's just that my arms started itching the day after I transformed, I tought nothing of it at first because it passed after i scratched them a bit, but it started again the day after" Shakara replied while looking at her arms, "After we returned to the castle, did you start training right away?'" Avaritia asked and Shakara nodded, "Then you're just tired, after you changed the skin of your arms you should relax a bit, the fact that you defeated a Furiko seconds after the change, tell you what, how about we go to the lake!"
And so Avaritia, Shakara and the rest of the group, head to the lake to take the day off and it was going well, they also invited Hatsu since she got entangled in the fight with the Furiko, they managed to find a formation of small islands in the middle of the lake, Starrow used her power to teleport them there, and they settled there (Yes they have swimsuits, except for Paint and Thinner cause... Slimes...), Avaritia, Starrow and Shakara were sunbathing, Dreamiv was lazing off under the beach umbrella, Paint, Thinner and Oracle were playing in the water, Hatsu was making water shows with her ability.
Focusing on the ones sunbathing, Shakara was actually feeling much better and the itch in her arms went away too, "I feel much better" she said feeling more relaxed than ever, "See? I told you it would go away like this" responded Avaritia, while they were talking, they didn't notice that there was something quickly falling to the ground, when it landed, it made them all look away from what they were doing to look at what made that noise.
"Where did that boulder come from?" Asked Starrow as she got up from her chair, "No idea, we're litteraly in the middle of nowhere." Answered Oracle who was getting closer to the boulder.
Thinner went up to the boulder and said "We can't just leave it here, just give me a moment I'll dissolve it", he then did as he said, but nothing happened, "What? Paint, Give me a hand!" Paint wnt to thinner and they fused into Black Stain, who was able to dissolve the boulder, but still with some difficulty, but he was done dissolving it, something unexpected happened.
Starrow froze, just froze... No movement, Avaritia tried waving her hand in front of her eyes, but still nothing, so Black Stain started getting close to Starrow, and that seemed to set her off, she turned into her enraged state and attacked Black Stain, but with him being a slime, she couldn't actually hurt him with punches, but something else happened, Black Stain started wrapping around Starrow's body.
Oracle and Dreamiv were the first ones to try and detach the two, but Starrow generated a light bright enough to blind them, and when she was done absorbing Black Stain, the light dissipated and a large puddle of black paint stained the center of the lake.
"What happened? Where are Starrow and Black Stain!? I mean, I think I know where Black Stain is, but Starrow!?" Shakara asked panickingly while looking around for Starrow, but she didn't have to look around for long, because from the puddle, a giant version of Starrow's enraged state jumped out, and covering it was a layer made out of Black Stain's body.
Here's the beginning of Starrow's Rampage, catch the reference?