Any rec for manga you cannot forget, like left a deep impression on you?(๑•ㅂ•)و�...

Oyasumi Punpun. It was quite a ride.

no. 6
also tsubasa reservoir chronicles/xxxholic (my icon is from there ヾ(❀╹◡╹)ﾉ~)

Hadashi no Gen, by Keiji Nakazawa. About a young boy who lives in Hiroshima during World War II.
If you manage to read through it till the final end, you'll never think of "war" the way you did before, however much a fan of world of warcraft or star wars or any other war fun you used to be...