- "Solving Miis' problems raises their happiness. Something neat might happen if you raise it high enough..."
- — Tutorial, Tomodachi Life
Levels are a side-goal in Tomodachi Collection, and Tomodachi Life. Miis will level up whenever their Happiness meter fills up, as a result of giving them food, items, clothing, and solving their problems.
When a Mii levels up, the player is able to give them bonuses:
- Songs: A Mii will be given a song that they're able to sing at the Concert Hall or, in Tomodachi Collection, directly in the mii's appartment. In Tomodachi Collection, the song genres are Idol, Enka, Rap, Ballad, Rock, and Pop. While in Tomodachi Life, The song genres are Metal, Pop, Rock & Roll, Rap, Ballad, Opera, Techno, and Musical. In the Japanese version, Enka is also included, but Techno, Opera, and Musical are excluded in return.
- Interior: A Mii can be given one of 6 interiors that are only available via leveling up. In Tomodachi Collection, These interiors are Country, Business, Middle Class, Natural Wood, Scandinavian, and European. While in Tomodachi Life, these interiors are Family, Modern Asian, Natural Wood, Plant, Polka dot, and Tiled. They will not appear for sale in the interior shop in either game.
- Gift: A Mii can be given a gift that they can use in their apartment and outside it. In Collection, there are only 8 gifts, allowing a single Mii to be in possession of every available gift. In Life, there are 28 gifts, allowing Miis to only carry 8 gifts total and trade one out if he/she wishes to receive another.
- Phrase: A Mii can be given his/her own catch-phrase, which they will say frequently as time passes. Additional catchphrases related to a Mii's mood are set through alternative methods.
- Pocket money*: The player gives money from their own pocket to the Miis. The player may choose any amount to give, and once a Mii has collected $10,000, they will use it to take a trip to outer space. Once the first Mii travels into space, astronaut suits become available for purchase in all their available colors.
In Tomodachi Collection, the Mii will possess every song, interior, gift, and a phrase by the time they reach level 22. Every level afterwards will result in the Mii giving the player a silver coin, which can be sold in the pawn shop for a very high value.
In Tomodachi Life, when a Mii hits level 20, regardless of what bonuses they were given previously, the player will receive two additional options:
- Clothing*:The player can give the Mii any item of clothing in their collection that has been acquired or have previously owned, without being charged any profit.
- Hats*: The player can give the Mii any hat or headgear in their collection that has been acquired or have previously owned, without being charged any profit.
After the Mii is given a bonus, he/she will give the player either a silver coin or a gold coin, which has a higher sell value.
The level cap is 99. Level 99 Miis can still level up as normal, but the number will not increase any further.
- The activity that gives the lowest amount of Happiness and money is a Mii waking up from hypnosis. The activity that gives the most Happiness and money is after a Mii gets a confession accepted, or after a proposal is successful.
- The Happiness will go down if the Mii doesn't like a food/article of clothing, especially if it is an absolute worst/worst ever.
- Unlike most games with level-up systems, it is pathetically easy to increase a Mii's level, as the amount of Happiness required to reach the next level does not increase as the Mii's levels get higher.