Here's a summary:
* Aizen's Invasion: During Aizen's attack on Soul Society, Momo Hinamori, Toshiro Hitsugaya's lieutenant, is severely injured by Aizen.
* Toshiro's Rage: This fuels Toshiro's anger and determination to protect her. He unleashes his full power and fights Aizen, despite being severely outmatched.
* Aizen's Manipulation: Aizen intentionally uses his powers to hurt Momo, provoking Toshiro and making him vulnerable to attack.
Important Note: While Toshiro protects Momo, it's not the *only* time he does so. Their relationship is marked by a strong sense of duty and care for each other, and he protects her from various threats throughout the series.