I entered graduate school in April (October). I received an ECS-ID notification in which the same ECS-ID I used to have is printed. Should I activate it again?
It is not necessary to activate it again as long as you remember the password. But if you don't remember it, you can set a new password by activation.
And also, please set email forwarding of Student E-mail (KUMOI) to your regular email address as well. You can set email forwarding on the same URL as for activation.
Activation and email forwarding setting website :
FAQ - SubCategory