Rank

As your rank increases, your maximum stamina increases, and your party can hold more companions.
At rank 51, your maximum number of friends seems to increase by 1.

Raw Table

Rank	Stamina	Party Cost
01	15	36
02	-	37
03	16	38
04	17	39
05	18	40
06	19	41
07	20	42
08	21	43
09	22	44
10	23	45
11	24	45
12	25	46
13	26	-
14	27	47
15	28	-
16	29	48
17	30	-
18	31	49
19	32	-
20	33	50
21	34	-
22	35	-
23	36	51
24	37	-
25	38	-
26	39	52
27	40	-
28	41	-
29	42	-
30	43	-
31	44	53
32	45	-
33	46	-
34	47	-
35	48	-
36	49	54
37	50	-
38	51	-
39	52	-
40	53	-
41	54	55
42	55	-
43	56	-
44	57	-
45	58	-
46	59	56
47	60	-
48	61	-
49	62	-
50	63	56
51	64	57