okay so i went trough the trouble to create Ukitake`s bankai and i think this pic will clear out a lot of the confusion its not an official bankai though just fan-made
- Spoiler:
Ukitake`s bankai takes the form of two twin blade`s formed of pure lightning, his outfit also changes slightly, there is a shallow ripple of water flowing around him like a defensive halo, it never leaves his side since this is no ordinary water but also a part of his bankai ability, the water flows faster the more reishi he releases and the more reishi is around him, seemingly defying gravity just like the other captains his immense spiritual pressure is released and will affect those weaker around him... whenever and in whatever mood he is in seems to affect the weather around him when he is in his bankai which is one of its greatest assets
Once an attack is tossed at his way his defensive field will activate and form into a bubble around him, it might look fragile but is actually very solid, this defense can also be used in an offensive manner the more reishi condenced into the the water the greater the defense respectively offensive power is... the defensive barrier will only activate if he can`t see the attack coming, almost as if it had a will of its own, however beings with higher reishi can seemingly break or penetrate this barrier assuming they put in enough effort, once the barrier has been broken it wont recharge for another 5 turns, (it has to be completley broken)
He can also shoot lightning jolts from his blades at will, with the speed of a real lightning and the size depending on how much reitsu he is willing to put into the Zanpakto. Trough the Zanpakto is more than 200million Volts easy... it can reach as high as 500million volts at best, due to the size and power of his Zanpakto he often desires to keep it sealed in its shikai rather than bankai during a battle since he fears its destructive power...
Careful scientific measurements of many lightning flashes have revealed that the electricity moves at different speeds at different stages of its journey in the lightning flash. Also, its returning upstroke is much faster than its downstroke. However it indicates a maximum speeds around 87,000 miles per second, making it extremely hard to dodge...
Let me know if this needs some changing...