The appearance of a science fiction story on AMV is unpredictable. It could be anytime based on factors like the creator's inspiration, available resources, and audience demand. So, you just have to keep an eye out for it.
In the manga, Senjumaru did not employ Bankai. The character's abilities and actions were depicted differently without resorting to this particular power.
For a love story AMV to be outstanding, it needs a well-chosen song that conveys the emotions of the story. Also, the editing has to be seamless, with smooth transitions between scenes. The quality and clarity of the video clips matter a lot too.
Shinji did use his Bankai in the manga. It was a crucial moment that turned the tide of the fight. The Bankai's power and unique abilities were showcased, adding an exciting element to the story.
One interesting 'harry potter bankai fanfiction' could be where Harry discovers a hidden power within himself that combines the magic of Hogwarts with the concept of bankai from 'Bleach'. For example, he might use it to defeat Voldemort in a more spectacular way than in the original series.
Another way is through character development. A character in Harry Potter, say Neville, could go on a journey to master a bankai - like power. This could involve him training in a special place, like the Room of Requirement, which could transform into a training ground similar to the ones in 'Bleach' for bankai training. He would face challenges and grow as a character, all while blending the two concepts.