Ok you'll have to forgive me here, because I never caught
the name of the main character of this movie. It's some tall
guy with short black hair in a beige trenchcoat-type thing.
Keita and Youko are having some kind of drinking party with
all the other Inukamis, and somehow they started stripping
their clothes. The man with the trenchcoat refuses, seeming to
be somewhat of a straight arrow, saying
he's not a hentai. The others insist he is, and he gets
kinda angry and leaves the party, muttering "I'm not a
hentai! I hate hentais..."

Flash forward to the next day, when his body is found by the
riverside. Everyone is extremely upset, and attends his
funeral. But two people are missing - Keita and Youko. It
turns out that they were waylaid on the way to the funeral
by many men wearing orange biohazard suits. These men are
pouring out of armed trucks and are attacking civilians, but
only a certain "type" of civilian. Yes, they are attacking
all the hentais! The orange suits are rounding up all these
men cosplaying and wearing S&M stuff. (And there seemd to be
quite alot)

Among these hentai men, there were alot of parodies. There
was a guy wearing a Haruhi outfit, a guy wearing a Nanoha
outfit, and many others. One of the guys did a Ouran-type
intro. Very funny. But they were all being beaten up and put
into trucks by the orange suited men.

Back at the funeral, the other Inukami were wondering why
Keita and Youko never showed up, and also speculating at the
strangeness of the beige-trenchcoat-man's death. One of the
inukami speculated that someone had used a "Desu" note (desu
was spelled in hiragana, but obviously parodying Death
Note). Quickly dismissing that idea, they figured out that
whatever had killed trencoat man was probably also
responsible for holding up Youko and Keita.

Meanwhile, Youko and Keita decide to help these orange
suited men after hearing of the hentai's plight. Keita goes
down to face them and immediately strips (elephant!) and
spends the rest of the big battle naked. All the other
Inukami magically appear at that spot to help him. He
confronts the orange suited men, and one rips off his suit
to address him as the leader. Turns out he's.....the man
inthe beige trenchcoat! The movie is put on hold while he
performs a wonderfully silly song about ridding the world of
hentais. After that, Keita asks him exactly what is going
on, and he tells this story...(and here's the part I don't
understand)...

Flashback!
As the man in the beige trenchcoat was leaving Keita's party
and muttering about how much he hated hentais, he was
carrying an object that looks like a small house. (I'm sure
this is something that people who watch the series would
understand). Then he slipped and the house started glowing
and tiny little people-blobs came out of it, all muttering
about how much they hated hentais.
Yes that's right, they turned into clones of the trenchcoat
man!

Back in the present, all the orange suited men rip off their suits and indeed, they are all clones of him, wearing bright white suits! And then they commence fighting all the Inukami. The clones are armed with swords of light and they are all good fighters. They pile on top of the Inukami a la Smith on Neo in the Matrix Revolution. The inukami manage to get a few hits in, but then the clones reveal their super ultimate attack! Yes, they join their bodies together in a very lewd way to form a super giant robot!

This giant robot is much too strong for even the combined strength of all the Inukami! On the edge of despair, Keita remembers something (that i dont get, something about a giant frog statue that he received from grateful frogs). The Inukami all go and get it, supporting its weight among them. Once it arrives, Keita takes control of it and has it shoot super red lasers from its mouth. With this power, the robot is finally defeated.

The clones melt away into nothing, and the Inukamis quickly hurry to the funeral to prevent the trenchcoat man from being cremated, as he is actually still alive! But as they get there, it just too late. His body is already in the fire. But wait! The door opens, and his naked body comes tumbling out, unburned and alive.

Everyone rejoices, and naked trenchcoat man embraces naked Keita, with the help of one rather large elephant face. All the Inukamis look at them weirdly and say, `Maybe they are hentais after all!`

Movie end! The entire cast sings a silly song while selected scenes of the movie replay under the credits.

It was alot funnier than I made it out to be. There:s no way I could recount all the jokes and funny bits that happened, there was just too many.

The Karuo's inukami decides to find his soul or something, I would really like to know what happens after that... Reading your summary of the movie... it's just a side story...