My three big achievements may not seem that big compared to some other people's, but they're still moments that I myself am quite proud of.
First Ever Clear: The first time I cleared a Touhou game was about a year after I had started playing. I had been trying for that whole time to get through EoSD 'cuz I wanted to open up the Extra Stage and fight Flan for myself. To this day, I still haven't unlocked it, but I'm still satisfied with my one successful clear of the game. I had been playing as MarisaB because... well... Master Spark. Why else? Anyways, I had just started on my last continue right as I got to Remilia, so I had a full stock of lives and bombs. By the time I reached her final spell, I was out of both. It was either capture the spell or lose yet again, and I had gone into the fight completely blind. Every time a bullet even so much as approached me, I clenched hard, and I was on the edge of my seat the whole time, sweating nervously. When I saw her health hit zero and the final results screen pop up, I jumped out of my seat and celebrated. It was a feeling of exhilaration I very rarely get anymore, and I doubt I'll ever forget it.
First 1cc: My first 1cc was on Mystic Square. It was on Easy (Yeah yeah, laugh it up. Just know that I despise easy mode mockery.) as Mima. It had been a few months after clearing EoSD, and I had been playing the crap out of MS. It quickly became one of my favorite Touhou games ever, and I just kept getting better and better at it. One morning that Summer, I got up and decided I'd do another run. The farthest I had gotten on one continue at that point was Yumeko, so I hoped to at least beat her that time. Much to my surprise, I actually made it to Shinki, and I was making solid progress through the fight. The longer it went on, the more excited and nervous I got. As I was doing the fight, my dad came down and started watching. He asked a bit about the game, and I answered his questions while trying not to break my concentration. When I won, I had to try not to cheer since the rest of the family was still asleep. It was an even greater feeling than the one I got from clearing EoSD.
Blind (almost) 1cc: Then there was that time a few days later when I nearly did a blind 1cc of Lotus Land Story on Normal. I went in as ReimuA, and absolutely demolished my way through the game. I only expected to reach Stage 3, 4 if I was lucky. I made it all the way to Yuuka's final attack in Stage 6 before losing my last life. She had only a sliver of health left. It was my most painful Game Over yet, but it gave me the determination I needed to try again. On my second attempt, I pulled it off, bringing Yuuka down and getting that good ending.
To this day, those are my three proudest achievements in any Touhou games. I have yet to open any Extra stages in Windows games, and I haven't cleared any of the ones in the PC-98 games yet. Even after I do, however, these three moments will be forever ingrained in my memory, fondly remembered as great milestones of my progress.