gen always needs to find some character to torture… i dont know if its kariya or sakura in f/z tho… in pmmm it was sayaka for example and in saya no uta the maincharacter… but woah there this idea with sakura fascinates me actually
There was an interview in one of the complete materials where Gen and Nasu talked about it. At the time Nasu had like 45% of Zero worked out, Gen came along and asked if he could write it and Nasu agreed, but after writing out the draft Nasu came across the part where Kariya was supposed to die.
Gen’s original idea was for Kariya to come back to the matou mansion after berserker’s defeated, Zouken appears, turns Sakura dark and then have her kill him. Nasu found this way too dark, and kindly asked Gen to change it.
Nasu’s also gone on record saying that, if he wrote Zero, Kariya would’ve gotten a happier ending.