Hazard Levels in Kamen Rider Build: Thresholds and Progression

Hazard Level is a measurement of a human’s resistance to Nebula Gas in Kamen Rider Build. It also indicates whether someone can safely use specific transformation systems. In the confirmed progression, Level 3 is needed for the Build Driver, Level 4 is needed for the Sclash Driver, and Level 5 is associated with the Evol-Driver. The level is not simply a combat rating: it also affects whether a person retains their human form after exposure to Nebula Gas and how strongly certain psychological effects influence them. These details are summarized in the Hazard Level reference.

What Hazard Level measures

Faust created the Hazard Level system to measure resistance to Nebula Gas. Lower levels indicate a greater risk of death or transformation, while higher levels allow a person to withstand exposure and operate more advanced Rider Systems.

The early thresholds are severe:

• Level 1: A subject has an extremely low tolerance and may die after exposure. A pre-existing illness can contribute to this result.
• Level 2: The subject is transformed into a Smash after receiving the gas. When the Smash is defeated, the person can return to human form, although short-term memory loss may follow.
• Above Level 2: The person can generally retain human form after exposure and does not suffer the same immediate transformation outcome.

These descriptions explain why even a small numerical increase can have major consequences. A reading above 2 does not automatically make someone a Rider, but it marks the point at which surviving Nebula Gas becomes possible.

Rider System requirements

Hazard Level also determines which transformation devices a person can use. According to data attributed to Gentoku Himuro and Takumi Katsuragi, the known requirements are:

The wording of the thresholds matters. The Build Driver is associated with a level above 3, while the Sclash Driver requires a level above 4. Reaching exactly the displayed value of 3 or 4 is therefore discussed in the source as an important milestone, but the practical descriptions frame the requirements as exceeding those levels.

Level 5 is particularly unusual. The available information states that the Evol-Driver requires it, but also suggests that an ordinary human may not be able to reach the level naturally. Ryuga Banjo later reaches Level 5 because of his alien physiology, allowing Evolt to possess him and use the Evol-Driver.

Known Hazard Level readings

The measurements recorded during the story show that Hazard Level can rise gradually rather than changing only at whole-number thresholds.

Sento Kiryu is measured at 3.2, later reaching 3.7. Blood Stalk notes that anger increases Sento’s reading, showing that strong emotions can temporarily affect the value. When Sento uses Rabbit Tank Sparkling, his reading reaches 3.9.

Ryuga Banjo begins one confrontation at 2.4 and rises to 2.7 during the fight. His determination and synchronization with the Dragon Fullbottle eventually push him to 3.0, allowing him to become Kamen Rider Cross-Z. Continued fighting as Cross-Z raises his Hazard Level to 4.0, which allows him to use the Sclash Driver.

Other recorded values include:

• 4.2: Kazumi Sawatari’s latest listed reading.
• 4.2 to 4.4: Sento’s reading before it rises rapidly during a later event.
• 6: Sento’s level after using a Pandora Box panel in the Build Driver.
• 6.3 or higher: Sento’s level after turning the Build Driver’s Vortex Lever with the panel inserted.
• 7 or higher: Ryuga’s level after remembering the destruction of Mars; Sento later reaches this range as well.

How Hazard Levels increase

The source identifies two theoretical ways to raise a person’s Hazard Level. Strong emotions can produce a temporary increase, as shown by Sento’s anger-related readings. Continual use of purified Fullbottles and Rider Systems may raise the level permanently.

This distinction is important when comparing characters. A temporary emotional surge may help someone pass a threshold during a battle, but repeated exposure to Rider Systems appears to create more lasting growth. The available material does not provide a universal formula, exact training schedule, or guaranteed increase for every user.

Effects beyond transformation

Higher Hazard Levels can reduce the psychological effects associated with the Pandora Box and Nebula Gas. Sento is able to use the Hazard Trigger for longer without immediately going berserk as his level rises. Gentoku’s paranoid and cruel traits, which developed after the Sky Wall Tragedy, disappear after experimentation by Namba Heavy Industries.

At Level 7 or higher, the increase also affects Fullbottles physically. Shinobu Katsuragi’s research states that two Fullbottles changed by this level can create a Best Match regardless of whether their contents are biotic or abiotic.

FAQ

Is Level 3 enough to use the Build Driver?

The confirmed requirement is described as a Hazard Level above 3. Ryuga’s rise to 3.0 is specifically connected with becoming Kamen Rider Cross-Z, while the broader Rider System data identifies the Build Driver threshold as above Level 3.

What is the difference between Level 2 and Level 2.1?

Level 2 subjects transform into Smash, while people above Level 2 can retain their human forms after Nebula Gas exposure. The source lists 2.1 and higher as the range where subjects retain their human form.

Who reaches the highest recorded level?

The supplied material records Ryuga and Sento at 7+. Sento is also recorded at 6 and 6.3+ after using a Pandora Box panel, but the later 7+ range is the highest listed milestone.

Is Hazard Level a permanent stat?

Not always. Strong emotions can temporarily raise it, while continued use of purified Fullbottles and Rider Systems is described as a possible way to increase it permanently.