It was a pretty hard decision, seriously. Key works are ALL sad.
I decided to exclude those that seemed the least likely to be the saddest. Well, I can’t judge those I haven’t read already so to me, it’s neither Kud Wafter nor Harmonia. Was Charlotte even sad? Oh right, there is the deaths of Ayumi and that long haired guy who’s always drenched whoes name I forgot but it’s not like deaths are inexistent in other Key works… Planetarian was sad but the only sad part was Yumemi getting broken so I can’t say that it’s the saddest. So, definitly not Planetarian or Charlotte. Kanon was sad… kinda… So was Air but… I can’t get myself to call either of these two the saddest. They are the only Key works that didn’t even make me feel like crying. Rewrite was pretty sad (Uuuu… Sakuyaaaaa, Esakaaaaa, Kotarouuuu) but it felt like the “sad” part wasn’t… important? Nah, it was definitly important but when Rewrite is mentionned, the sad parts just don’t come to me first and I need to particularly remember them to feel like crying… All I can say is that it didn’t feel like the saddest of them. Angel Beats has a pretty sad story but I only watched the anime which didn’t feel all that sad. I expect that the VNs would be WAY more sad but I have yet to read them. Tomoyo After was pretty sad but calling it the saddest wouldn’t feel right to me so I’ll just exclude it.
And so… That leaves me with two VERY hard choices: Clannad and Little Busters. They were both really sad and the closest to make a tear fall from my eyes (I’m not the type to cry because of a story). However, I’ll go with Clannad. Why? Refrain in Little Busters was definitly the saddest route of all Key. However, except for Haruka’s and Kurugaya’s routes (I haven’t read EX so I don’t know about the EX routes), the heroines’ routes weren’t sad, at least, they wouldn’t compare to Clannad’s routes that were almost all equally sad and heartbreaking. So, yeah, Clannad’s the saddest for me.
…How many times have I written the word sad I wonder… I’m too lazy to count.