Smile, codenamed Number Four, emerges as a key antagonist within the Thousand Spirits Group’s Numbers Elite. Forged through brutal physical training under Card Sensei (Number Five), he developed a ruthless combat philosophy, rejecting his mentor’s gentler tactics in favor of merciless efficiency. This resentment fuels his bitter rivalry with both Card Sensei and protagonist Bashin, whom he perceives as a barrier to validating his supremacy.

In the anime, Smile manipulates J into joining the Thousand Spirits Group, forming a temporary alliance driven by obsessive possessiveness over J and a fixation on showcasing their destructive synergy. His yellow attribute clashes ironically with his villainy, subverting the "light is good" trope. A master of psychological warfare, he taunts adversaries over personal weaknesses, exemplified by his cruel jabs at Masako (Number Eight) about her unrequited feelings for Card Sensei. After a decisive tag-team defeat by Bashin and J in Isekai World, he reemerges brainwashed under Number Nine’s command during the King Uchuuchouten Cup.

The manga amplifies his threat, casting him as the primary antagonist who traps Bashin’s team in an alternate dimension where Battle Spirits victories dictate freedom. He weaponizes J’s inner turmoil to destabilize the group, only to fall to Bashin’s resolve and allied teamwork. Both versions depict him relentlessly pursuing dominance, sparking friction with allies like Number Nine due to his self-centered schemes.

His unsettling persona is accentuated by a signature coat cape and a shrill "kekeke" laugh. Though his origins and motives remain minimally explored, his persistent role as the protagonists’ foil highlights themes of rivalry and toxic mentorship. Post-defeat, his fate lingers unresolved, yet his legacy endures through the psychological scars and strategic hurdles he imposes on the cast.