Let's see how accurate I am. :)
HOW I PREDICT ES21 WILL END:
Just as Mamori is opening her scrapbook to the appropriate page, Hiruma comes up and surprises her/makes a crude remark! This sets off some absolutely darling comedy as the two begin to bicker.
For some reason, every single character in the series will skip class at their own school to come and screw around at Deimon FOR NO REASON WHATSOEVER. (The explanation being, of course, that Hiruma invited them, though specifically why will still not be elaborated. It will be left to be assumed that it's some sort of World Cup celebration of winning/trying their best, despite the fact it will also be hinted that the Cup finals ended a very long time ago.) So of course, we'll get to see our last Takami-Sakuraba-sweatdrop at Otawara, Mizumachi striptease, Kotarou screaming at Akaba as he charmingly strums his guitar, Kisaragi sparkling at Gaou, more sweatdropping from the more "serious" and "cool" characters, and other such hilarities.
There will be unneccasary hand-holding on the part of one manager-quarterback couple in particular... that's right... Marco and Maria! :D And maybe Kotarou and Juri, as well as a pairing we didn't totally see coming that will upset everyone reading. Perhaps some HiruMamo, but likely not, and so the fans will bitch and weep endlessly so that the fandom goes out in a miserable fart of unrequited love.
At least once, Monta will hit on Mamori (who will, as usual, be polite) and the HaHa Bros will say something clever in response to his failure. Sena will say "HIIIII" at least six times, Musashi's father will be magically healed, and Ikkyu and Monta will have some hilarious routine involving aerial battles and fighting for Mamori's love (followed by more HaHa). Agon will show up and say something like "C'MON TRASH LETS BEAT UP STRANGERS", which will very subtly hint that he and Hiruma have made up and are friends again. Unsui will be in the background, rolling his eyes, and will perhaps even scream at his brother and drag him off-screen by his ear; all we can be sure of is, if he does make an appearance, he'll still be wearing his monk cosplay school uniform.
Hiruma's dad will appear, he and Hiruma will have a moment, and then he will proceed to mistake Mamori for his son's girlfriend, to which she will adamantly deny. Oh, the unpredictable hilarity!
Shin will be training vigorously, followed by a series of social faux pas geared towards Sena that will make fangirls melt and fanboys cry tears of manly idolatry. Ishimaru and Yukimitsu might even make appearances, if anyone even remembers they were apart of the series at all, which they won't (Yuki, maybe, but Ishimaru? Eh...). Someone will try to bring up the World Cup, and just as the readers began to hope for something beyond a cliffhanger, something like Hiruma firing his guns will so completely enrapture everyone's attention that they forget completely what they were talking about.
The chapter will end with a group shot of them all being hilariously true-to-character, captioned with a sentimental and meaningful monologue by Sena.
...I wonder how accurate I'll turn out to be? (forgive the biting sarcasm... this came out less light-hearted than intended...)