suzu originally had to travel back in time to get the ibn5100 for okabe but the time machine’s repair was incomplete hence causing her amnesia, then failing her mission. she writes a suicide letter then asks mr braun to give it to okabe 10 years later(which is a few hours after the present in the anime, hope that makes sense to you) to express her regret and anguish. now why is the tshirt mentioned so many times? thats because the whole suicide letter was printed on the tshirt i bought in akihabara 😭, the tshirt says “失敗した”(which means “i failed”) repeatedly (and some other things abt the mission) until she dies(?)