This comic is fairly obvious, even for the plebeians out there, but the third panel requires some special explanation.

A current trend in anime/manga is to have one character be a "tsundere" type, that is, a character who acts rudely or uninterested in the main character, but who actually cares deeply for them, occasionally doing nice things for them and then ascribing a vapid excuse for their out-of-character behavior. In a way, this adds a bit of verisimilitude to the story, since relationships in real life are generally not honest but rather built upon quick probings into someone else's feelings until you feel secure enough to admit your feelings truthfully.

Now, the third panel, with the character attempting to summon "Hitler", is well known as a "tsundere" type character: overbearing, bossy, but with a delicate heart at her center. Her choice of Hitler as her Persona actually says a lot about her, well, persona: she attempts to put forward an image that will drive others away, because (like Hitler) she is afraid of falling in love.

It is, of course, a matter of historical record that the non-aggression pact between Hitler and Stalin was eventually called off because of Hitler's 'confused feelings' for his Russian counterpart. A man with world conquest on his mind could hardly share his power with a non-traditional partner, and thus history was made.

Thanks for that explanation TORU, now would someone explain what the fucking joke is?

I don't know. Are the "Welcome to the..." comics supposed to be funny? It seems like they are trying to be, but are only getting about 50% there. Or they have more panels than the jokes deserve?

"Welcome to the.." comics are like Choose Your Own Adventure books. You decide which panel is the 'real' joke. You're the man. You got da powa. Persona-sama don't roll with the staid cartoonists who insist on introduction-setup-question-punchline. Each panel is a look into another universe of activity, and by looking at each panel, you temporarily pop them into our reality for the breadth of a second.

As more and more personas disappear and give way to ever-growing populations, both the wild (Hitler) and civilized (Ali) will collide. The vacuum personas leave will begin to "leave presents on the front lawn." Peace of mind alloted critters like a wolf, coyote or a fox is more apt to do damage.

In other words, standing and suiciding in the same spot for long periods of time can cause mess piles. Miniature mounds. Divide the number thirteen.

What Toru has said is indeed absolutely correct, but what he fails to explain the is the 'fucking joke' that fair lech is attempting to uncover.

Admittedly, the revelation of the Tsuendere female is nothing special, given that this is a normal element of everyday experience. Much the same, Shakespeare's plays were structured on the common experiences of life, but this is not what made such plays like Othello as funny as they are.
To put it plainly, recursion is the core element of the joke. The joke is revealed in that third panel when Mitsuru appears to summon Hitler, which as we know, summoned one of the first personas himself. Although Hitler had studied the arcane arts for several years, his form was crude and imperfect, preventing him from manifesting the directly material persona that would have ensured his victory. Instead, Hitler was forced to summon what many of us would call a 'meta-persona,' one which is not exactly material, but still 'present' enough to ensure that Hitler himself would triumph not over the physical bodies of his opponents, but their minds and memories. As a result, Hitler essentially summoned his own means to enact his own summoning by summoning himself into a collective awareness of himself. To put it plainly, Hitler's summoned persona was within all of us, so to speak.

Once this is realized, one can decipher the reasoning behind each of the character's summonings. Akihiko summons Mohammad Ali as his Persona, essentially summoning the Persona responsible for his own conception. Aegis too follows this same pattern, summoning Robocop, the first ever built true-android.

Junpei's choice to summon the Japanese Gravure Idol Nonami Takizawa (Affectionately known as Nonamin or 'Takizawa-san') has no actual relevance to 'the joke,' and merely serves to highlight the artist's sexual preference in a way that would seem as if he were saying "Hey everybody, I'm aware of this female."
Without a doubt, this is a sign of the artist's first true sexual awakening as this is the first time that he has ever referenced to such subject matter in his works.

So the joke is that it's a tedious load of pretentious wank. Err, thanks.

Oh, no, I believe that you may have misheard me.

The joke is that the characters are summoning their progenitors in a sort of 'circular definition' way.

The characters are accusing MC of "making up" the mythologically-derived Personas that are a part of him, so Junpei summons Nonami Takizawa because he's joking that a Japanese model is his mythological hero. The others follow suit.

Akihiko summons Muhammad Ali because the former is a boxer.

Aegis summons Robocop because she's a robot.

Mitsuru summons Hitler because of http://i27.tinypic.com/2a78sg2.jpg

I know you guys are making a joke out of unfunnily deconstructing a joke, but perhaps you're going way overboard here...