Natto is a climbing game for two players that can be played with a deck of 37 playing cards:

A-9 of spades, hearts, and clubs
4x Jokers, called flowers
2x each of J♤ , Q♡ , and K♧ , called the dragons

The player to win some number of pre-determined rounds wins the game.

The deal

Each player gets a set of the available dragons
Shuffle and deal 13 cards to each player
Remaining cards stay out and are not looked at

The deck

Card ranks are: Joker < A-9 < Joker < J♤ < Q♡ < K♧
- Flowers can be either a zero or a ten and take on any suit needed to complete a combination.
Suit ranks are: ♤ < ♡ < ♧
Dragons are wild and can stand in for any rank of the same suit
Bombs beat any regular combination or lower bomb
- J♤ Q♡ (lowest)
- J♤ K♧
- Q♡ K♧
- J♤ Q♡ K♧
- Joker Joker Joker
- Joker Joker Joker Joker (highest)

Sets

Sets are a group of 1-6 cards of the same rank including wild dragons. A set can be bested by a set of the same size with a higher rank or by the same rank of a higher suit.

Seqs

Seqs are groups of 2-6 cards of the same suit with increasing ranks. A seq can be bested by another seq of the same size, with a higher starting rank.

Imaginary seqs

There is a special type of seq called an imaginary seq that starts with a flower card followed by some number of dragons. An imaginary seq technically has no suit, so any and all of the dragons may participate in it. In the case where dragons are used to represent the same logical seq, the one with the higher ranking dragons wins.

Sums

Sums are groups of 3-6 ranked tiles (no dragons) where all but one of the ranks are added together arithmetically to equal the final tile's rank. Sums are only bested by sums of the same size containing a higher ranked total, or the same total of a higher suit.

Tubes

Tubes are groups of three consecutive pairs (with or without dragons) in natural order. Only tubes with a higher starting pair beats another tube.

Plates

Plates are similar to tubes except that they are groups of two consecutive triples (with or without dragons) in natural order. Only plates with a higher starting triple beats another plate.

Rule variations

Fewer bombs

Instead of six possible bombs, you can reduce the number to five by removing the double-flower bomb combination.

A single must end

Exhausting one's hand must be done via the play of a single to end a round.

Widened sums

Instead of requiring that sums match their lengths, you could also play such that only the total need be the same.

Shared dragons

Dragons are placed in three piles of each face card and publically available on a sliding scale: a player may only play a dragon combination that is maximally one tile larger than their opponent's largest dragon combination played so far.

Stricter shared dragons

The sliding scale can also be stated more strictly as: a player may only play one more dragon combination then their opponent and the playable combinations are limited to those that are maximally one tile larger than their opponent's largest dragon combination played so far.