Oneofakind Marshmallow custom rom for Xperia S is based on AOSP and it is focused on battery conservation, performance and stability. It is very lightweight rom that offers a smooth scrolling experience on your device. Besides, it is a packed with a whole lot of other features that you're gonna love.
This rom is already rooted, so you need not worry about rooting your LT26i after flashing the rom.
How To Flash Oneofakind Marshmallow rom on Xperia S
How To Flash OneOfaKind
Because the data partition of your Xperia S device is small compared to the required partition size, the device has to be re-partitioned in order to fully and properly accommodate this rom.
Now, before you proceed with re-partitioning the device, download the requirements (rom and gapps) above to your drive. Click here to learn how to re-partition and flash Marshmallow roms on Xperia S.
If you have any questions, please post in comments section below.