@Xystus Yea just like what another user said, its not how you would phrase it in English. If you want to indicate the past tense after a certain action is done, you don't use "was" with "to", instead use the past tense of the action (in this case, brought or gave) to imply that the action of "bringing the umbrella" has been done. In this case however, using was and to together implies that bro planned to do something (bring an umbrella to his sister) but ended up not doing it, delaying it, or doing something else entirely (say, talking to Tsuyu on the bus stop), which is not the case here as Chie clearly thanked his brother for bringing her an umbrella in the end.