How about a little +1 attack +1 defense buff the day after you lose? Let's say the determination to win by force and which will later change under the actions of Luciella?
i doubt that the dev is going to implement any sort that makes the game more difficult to balance.
The Dev tries to create a challenging, balanced game. (thats what i like the most in this game)
EXP gain is limited, so that you don't get overpowered, or that the dev has to balance the pace (exp earning) of the game.
Right now we can tell exactly how much attack and on what level you can be at max, e.g. when starting Nephlune quests.
So its much easier to balance and not make it boring (too grindy or too easy)
Rewarding deaths, would make it too easy, especially if you consider, that it also takes 1 day to upgrade +1attack +1defense with materials. And also that death doesn't cost any gold.
Think of, it it takes 4 days to read a book for +1 attack.
In the same time you would have gotten +4 attack and +4 defense.
And even if you say, lets tweak the numbers, it would add more complexity for the balancing.
EDIT: ok i see, you mean a buff that lasts only 1 day. Sounds fair. But on the other hand, there is an easy mode if you find normal mode too challenging.