Reasons
- to take a life
It is a very sad thing, when one has reasons to take a life. Is it worse when the same reasons prevent it? (Not exactly canon with the reveal of Gin's true intentions in the manga)
Duty
Rangiku Matsumoto had a strong sense of duty. Duty to the the Gotei Thirteen, first and foremost, she believes. Duty to her captain. Duty to Division Ten. She could never be accused of lacking a sense of duty, despite her occasional - well to be fair, near constant - procrastination of paperwork and an attitude to alcohol befitting a member of Division Eight. However, in the days, weeks... months... following the betrayal of Aizen, she sometimes wondered, when the hour was late and she was alone in her quarters - perhaps, though she couldn't say, in times when she was also inebriated - if the extent of her sense of duty - is it enough? - allowed her to despise Gin Ichimaru like the traitor he revealed himself to be.
Do I have the strength? Would I... could I... kill him with my own hands?
She licked her lips, suddenly dry, raised the dish of sake to her lips once more, and took a sip. Then, a gulp. With a slight sigh, she raised the whole bottle on end and tipped it all into her mouth.
'Ichimaru.'
She faces him on the battlefield, his half smile taunting, his eyes almost seeming to open. She strains to see, to see who he is, what he is, on the inside - but there is nothing but that ambiguity which she has never been able to understand.
'I will take your life, it is my duty.'
That smile only widens.
'Ran-chan, you cannot.'
And so, it is true. Rangiku cannot kill him for duty. No matter how desperately she clings to her duty, to her division, to her captain, to, she tries to convince herself, 'first and foremost' the Gotei Thirteen... it is not strong enough to overwhelm her duty, before all else, to Gin Ichimaru.
Fear
Gin Ichimaru feared. Of course, to reveal his fears would be very foolish, which was the reason why he did not. In fact, he considered himself quite accomplished at masking his fears from others - he thought it strange how much could be kept hidden simply by taking some time to smile.
To himself, however, he would not lie the fears away, nor smile them away, nor shut them away by simply refusing to look. Not that he had not tried to do so - oh he had tried - but he knew it wouldn't keep the fear away, in the end. As a sensible person probably would, he had wondered on how to rid himself of his fears. Among these fears, the most important one, perhaps, though he would not say - and perhaps it was not? - was Rangiku Matsumoto.
If he could rid himself of his fears - in particular, this one - then he would, no doubt.
'Ikorose, Shinsō.'
Shinsō's blade shoots forward and Gin smiles. It is almost a habit. Perhaps it already is. Then he makes the mistake of looking.
'Gin,'
and it is all she needs to say, because Gin is no longer smiling.
Gin cannot rid himself of his fear, because his fear of Rangiku Matsumoto is born of a fear for her. His greatest fear - which he may think, while safe in his mind, without any lies or smiles to veil it, to ignore it and push it away - means he cannot kill her for fear, because it is a fear of harming her.