Onee-sama is the closest term I can think of in the English lexicon shorter than "beloved older sister" which would be blisteringly long and not communicate it enough.
...And included a joke note container too :D
FAILEDArrestedI should had warded moreMissionGreetings everyone, I'm Morgana, a professional fallen angel.6Look, onee-sama! This flesh is forever yours!Pwugh...This is a memorable day indeed, I finally get to see the onee-sama who occupies my every thought.You're sick!You won't escape! Today I will become one with onee-sama!Can I just kill her here?Let me help you with that troublesome armour first...YrreeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaggghhhhCan't believe I got ganked in this wondrous momentOfficer, please take her away, and never let her loose on anyone else.Just the last frame is perverse enough.