This is my first ever question to this site and I'm still a beginner in Japanese, so forgive me if there's any mistakes:
So, I have been trying to translate this comic as a sort of practice for learning Japanese using Jisho and Deepl machine translation, and the two things that have been giving me the most are the ones mentioned in the question's title.
I have tried translating かつて生きた最後の夏 as [The last ever lively Summer] or [And the last Summer that I ever lived] which Deepl conjured up with something similar, but I still have a nagging feeling that's wrong.
As for 最初で最後の一日だ, I translated it as [The one and only time/chance I had, this day.]
The の一日 was what giving me the most trouble with that particular sentence, and I tried to compromise with my translation.
Again, I'm still an absolute beginner regarding Japanese so forgive me if there was any mistakes. What's the correct way of translating those two particular sentences?