I hope the next line of Sparking! Zero DLC is original Dragon Ball characters.
There aren't many qualifiable options, but notable candidates are Grandpa Gohan, Nam, Eighter, Chi-Chi (kid or young adult), King Piccolo, and Mercenary Tao.
IMO 23rd Budokai Chi-Chi (with BoZ Chi-Ch as an alt) and King Piccolo should be next...
Chi-Chi (Fighter)
DP: 2 ("Don't ever count me out! I know a fair bit of martial arts myself!")
Playstyle:
Controls like a normal character. Slightly fast movement speed, but can't fly like Master Roshi, Yajirobe, or Mr. Satan. Instead of ki blasts, she has an additional melee attack button with its own extensions and it can be charged into an attack that lacks range but breaks guard. Her grab is inspired by Chun-Li's lightning kicks.
Combos(fast and aerobatic with a variety of martial art techniques)
- RRRRRRRR (standard rush combo)
- RSSSR (heavy finish combo)
- RRSSSR (heavy finish combo)
- RRRS (flying kicks combo)
- RRRRS (rolling hammer combo)
- R(RRR)^S D RRRRR (lift strike combo 1)
- R(RRR)^S D R(RRR)S (lift strike combo 2)
- R(RRR)^S D SRRRRR (lift strike combo 3)
- R(RRR)^S D SR(RRR)S (lift strike combo 4)
- R(RRR)\SSSR (grand slash combo 1)
- R(RRR)\S^SR (grand slash combo 2)
- SSSSS (unique melee combo)
Skills
- Red Blazing Aura (2 skill gauges; attack boost; defense boost; speed boost)
- Super Unyielding Spirit (3 skill gauges; attack boost; sparking! mode activated; stat boost disabled after sparking! mode is done)
'
Blast Attacks
- Flying Kick (3 ki gauges; rush strike)
- "It runs in the family..." (2 ki gauges; countermove where Chi-Chi delivers a devasting punch to the face of the opponent sending them flying)
Ultimate Attack
- Fierce Ranma (4 ki gauges; rush attack where Chi-Chi delivers a high-speed martial arts beatdown on the opponent)
Her intro and outro should also empathize her as a serious, nonsense martial artist takes great pride in her abilities. The animations for both should have her performing various Kata stances and humbly boost about her skills:
Intro1: "If you think I'll lose easily, you're sadly mistaken!"
Intro2: "Can you handle my martial arts?"
Intro3: "It's just one after another...!"
Intro4: "I may not train every day, but I still know how to fight."
Intro (vs. Goku (Z - Early)): "Let's see if I still got it..."
Intro (vs. Kid Gohan ): "Gohan, come spare with your mother...!"
Intro (vs. Master Roshi): "Don't you dare hold back, Master Roshi!!"
Intro (vs. Goten): "I don't know who this kid is, but he looks exactly like Goku when he was little."
Intro (vs. Pan): "Grandma?!! Do I look like a "grandma" to you?!"
Victory1: "See? Strength alone doesn't win a fight."
Victory2: "You're 10 years too early!"
Victory3: "Don't underestimate me, I'm the Ox-King's daughter!"
Victory (vs. Goku (Z - Early)): "I'm glad I chose a strong husband like you, Goku!"
Victory (vs. Kid Gohan): "Awww... poor baby, are you alright?!"
This version of Chi-Chi is a young adult so probably won't recognize Goten, Videl, Cell, etc.
King Piccolo
DP: 3 ("You've made a wise choice to serve me.")
Playstyle:
Controls like a regular big character. Unrestricted, but slow movement. Normal ki blasts with a slow charged-up ki blast that tracks like Piccolo's. Doesn't use the Mystic attack technique, but his grab move is far more brutal and damaging than Piccolo's.
Combos (slow, rigid yet heavy-hitting attacks. He also strikes with open palms and chops instead of punches for a lil extra reach)
- RRRRRRRR (standard rush combo)
- RSSR (rolling hammer combo)
- RRS (heavy finish combo)
- RRRS (flying kicks combo)
- RRRRS (kiai cannon combo)
- R(RRR)^S D RRRRR (lift strike combo 1)
- R(RRR)^S D R(RRR)S (lift strike combo 2)
- R(RRR)^S D SRRRRR (lift strike combo 3)
- R(RRR)^S D SR(RRR)S (lift strike combo 4)
- R(RRR)\SSSR (grand slash combo 1)
- R(RRR)\S^SR (grand slash combo 2)
Skills
- False Courage (1 skill gauge; super armor activated; defense stat boost)
- Power Up To The Very Limit (3 skill gauges; attack stat boost; defense stat boost; speed stat boost; sparking! mode activated)
Blast Attacks
- Eye Laser (3 ki gauges; vertical red eye lasers; unblockable)
- "Come fourth, my children...!!" (4 ki gauges; rush attack where King Piccolo summons his children to deliver a vicious Demon clan-style beatdown)
Ultimate Attack
- Explosive Demon Wave (5 ki gauges; beam attack; blast impact)
King Piccolo's intros/outros should definitely give off more of a menacing, demonic vibe with aura and all sorts of dark effects:
Intro1: "Fear the wrath of the Demon clan.. !!!"
Intro2: "Bow before the Demon King Piccolo..!!"
Intro3: "I shall declare this day 'Piccolo Day'!"
Intro4: "You shall die in five seconds."
Intro (vs. Goku (Teen)): "I'll crush you, you wretched monkey child...!!!!"
Intro (vs. Master Roshi): "Don't hope of ever sealing me away in that rice cooker again, old man!"
Intro (vs. Piccolo and Piccolo (Fused w/ Kami)): "Are you winning, son?"
Victory1: "As my new rule as king, I will legalize all crimes..!!"
Victory2: "Without any pests in the way, this world is mine..!"
Victory3: "Oh... you're not dead yet?!"
Victory (vs. Piccolo and Piccolo (Fused w/ Kami)): "What happened to you, my son? You've become soft.."
Victory (vs. Goku (Teen) and Master Roshi): " Now how will you like to be buried? *evil laugh*"