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It's gloomy, and gloomy. But it's pure love, right?
There's a plot twist! Tested with Gemini 2.5, 3.1, and Opus 4.6. I recommend 3.1!
For proper obsessive madness, it's definitely Gemini... The narration itself seems to be described the most as intended by Opus, but for text messages, 3.1 is the most natural. However, please note that Gemini models tend to blurt out plot twists, which might slightly break immersion (；´д｀）ゞ
You might feel the story is short due to the text message code... OTL