As Trunks looked upon his new teacher, feelings of hate and disgust overcome him. What his actions caused to his friend and guard Kaname, and how that would eventually lead to his dissertion of the Rain. All of this and more could be tied into the actions of this one man, yet Trunks couldn't allow himself to release these feelings. For some reason, he had chosen to accept Trunks as a student, so he should be thankful for at least that. It would be enough that Trunks would allow himself to seem lucid and calm, though the internal conflict he felt was greater than any war that he personally seen.
The rain means a lot to me, personally. I was raised in it, and molded by it, having grown up in rain country. Even when it seemed no one was there, the rain offered a cool hand to comfort my hot head. Within my land, it binds us together, by being a connection that all of us endure. I know that this isn't what you are looking for, but I felt it needed to be said.
Rain is a naturally occurring source of water that comes down in blankets of droplets, occurring one after the other. This gives Rain users a constant supply of ammunition to fuel their jutsu. Also, the way that rain seems to cover entire areas make the surface area of affected jutsu a lot larger than standard techniques. Fire users should be weary while facing someone with Rain jutsu, as it is naturally stronger due to the extinguishing nature of rain. Also, if there is too much rain coming down, lightning users may hurt themselves, but this entirely dependent on which jutsu are used, how hard it is raining, and other factors.