Atypical mitotic figures (AMFs) are a clinically important indicator of abnormal cell division, but their reliable detection is challenging due to morphological ambiguity and scanner variability. In this study, we investigated three variants of the pathology-based model UNI2 applied to the MIDOG2025 Track 2 challenge: (1) LoRA + UNI2, (2) VPT + UNI2 + Vahadane Normalizer, and (3) VPT + UNI2 + GRL + Stain TTA. We found that integrating visual prompt tuning (VPT) with stain normalization improved generalization performance. The addition of test-time augmentation (TTA) using Vahadane and Macenko stain normalization achieved the highest robustness. The final submission achieved a balanced accuracy of 0.8837 and an ROC-AUC of 0.9513, placing it among the top 10 teams on the preliminary leaderboard. These results suggest that combining prompt-based adaptation with stain-normalized TTA is a promising strategy for classifying atypical mitoses under a variety of imaging conditions.