I don't actually have an idea about this, whatever it is. All I know is that Arashi's going to host this year's 24 Hour TV, which they also hosted 4 years ago.
24-Hour TV is an annual charity based program held first in 1978 by Nippon TV to commemorate their 25th year in the business. The aim of the charity program is to show the rest of Japan, if not the world, about the present condition and challenges faced by many regarding social welfare, the environment, and natural disasters. -- Here for the full article.
I have read that it is a day-long telethon where the featured artists are to stay awake for the whole 24 hours of the show and gather as much pledges as they can, where the funds will come from aside from the items that are up for sale like t-shirts, pens, et cetera.
There are also heart-warming segments about each host's task, usually featuring some of those who aren't as opportunate as us.
The show also includes a real life drama, like MatsuJun's "Myu no Anyo, Papa ni Ageru" for this year, which is about a father having a disease that took his ability to walk.
Then the one which made Aiba dearer to my heart, the letter-writing segment where one of the hosts writes a letter addressed to his groupmate/s (or at least that's what I know)
Four years ago, Aiba made this letter for the rest of Arashi about how much he appreciates everything that they've done for him and that despite of being sickly he'll try to do his best because he sees that everyone is giving it their all.
That's about it. That's everything I know about the program.