New Headcanon Book

River City Rampage (River city)

After River city girls 2, strange events began to ramp up the everyday school life of misako, kyoko, kunio and riki as the magic reactor Destruction led to the opening of different universal gateways. though a strange god know as Iv'buthun appears and ready to cause some havoc, it's time for the river city kung fu fighters to save their home from the god

New character: Skullmageddon, Former Evil overlord now joins the fight in saving the city, The Main character of River city rampage 
fighting style: Sword and Summons 

Crossover characters :

Sin kiske (Guilty gear): Hearing his uncle sol badguy entered the river city in search of fortune, Sin kiske joins in for the fun and new opportunities 
Fighting style: Fist and Flag 

The stranger (Furi) : After the end of Furi, The stranger ended up here in river city, armed with sword and gun, he is willing to find a person he knew
Fighting style: Sword and Gun

Yohei (Grimoire of zero) : Zero isn't sure how that works but yohei is gonna fight it out
Fighting Style: Giant sword and fist

Sanford and Deimos (Madness combat): After being separated from hank, Sanford was shocked to see deimos, alive and kicking and his body parts replaced with stones, without doubt, both duos are ready to fight.
Fighting style: Gun and hook (Sanford), Magic and Fist (deimos)

The Denliner imagin (Kamen Rider Den-O): Welp Denliner fuse blow out and needed a new one, momotaros just shouts "F***"
Fighting style: Sword - Momotaros, Rod/improbable weapon - Urataros, Axe and fist - Kintaros, and Gun and breakdance - Ryutaros, formal combat - Sieg

Secret characters:

Kamen Rider Ex-Aid / Emu Hojo:
Unlockable character - Reach 50 combo without being hit
And find the Cartridge named "Mighty action X"
Fighting style: Video game weapon style

Axel Stone ( Streets of Rage ) :
Find the missing bandana and defeat Axel stone *Superboss*
Fighting style: Similar to his streets of rage counterpart but added in Chi/Chakra Style *Which allows his grand upper to become Grandeur upper*

Baruuk (Warframe) 
Unlockable character: Find the Dojo and fight Mirages of Baruuk
Fighting style: Reluctant Monk